Historical Document · 1953
Early Work on Dial Telephone Systems
History of early dial systems including Strowger.
Historical Document · 1953
History of early dial systems including Strowger.
Early Work on Dial Telephone Systems R. B. HILL General Staff The first commercial telephone exchange, employing one operator, was opened for service at New Haven, Conn., in January, 1878, and within a short time exchanges had been established in a number of cities throughout the country.~ Ahnost immedi- will be moved past spring M, and four makes and breaks of the battery current will take place. These will attract the armature, a, of electromagnet b, at the distant station (b) fcur times, and, by means of pawl F, will give four movements to ratchet wheel G, ately, and, of course, long before the require- thus advancing the pointer of the receiving ments of the switching art were clearly envisioned, inventors in many walks of life began devising schemes for performing the sWitching operations by machines instead of by operators. The patented art in any new development is usually well in advance of the commercial art, and in the early work on dial exchanges, many of the fundamental ideas came from inventors who were without technical training or practical telephone dial (c) to letter D. In this way, the telegraph message was spelled out, letter by letter. The modern type of finger-wbeel dial experience, and whose mechanical arrange- ments for embodying their ideas were apt to be impractical or unworkable. Dial telephone systems derive their name from the use of a dial, Or equivalent device, operated by a subscriber or operator to produce the interruptions of current that direct or control the switching process at the central office. The use of a dial for such purposes, however, is much older than the telephone. It was suggested by William F. Cooke in 1836 in connection with telegraphy, and was first used in Professor Wheatstone's dial telegraph of 1839. During succeeding years, it was the subject of many improvements, and was employed not only in dial telegraph systems, but in fire alarm and district messenger systems. Figure 1 shows Froment's telegraph transmitting and receiving dials of 1851. When the pointer P of the transmitting dial (a) is moved to the letter D, for example, four teeth of wheel R ~ REcORD, February, 1931, page 265. 22 - an important mechanical improvement over the pointer type of dial - did not appear until 1896. The first dial telephone exchange patent, No. 222,458, was applied for on September 10, 1879, and issued on December 9, 1879, jointly to M. D.. Connolly, of Philadelphia; T. A. Connolly, of Washington, D. C.; and T. J. McTighe, of Pittsburgh. Although this first system was crude in design and limited to a small number of subscribers, it nevertheless embodied the generic principle of later dial systems. At each station, in addition to the telephone, battery, and call bell, were a reversing key, a compound switch, and a dial (Figure 2a) similar to that employed in dial telegraph systems, and bearing on its face the numbers corresponding to the different stations of the excbange. At the central office (Figure 2b) were ratchet wheels: one wheel for each station, mounted ODe above the other on a common vertical shaft and carrying wiper arms which moved with the ratchets. Actuated by the circuit interruptions made by the calling subscriber dial, an electromagnet stepped the wiper arm around to engage the contact of the called subscriber line. Although the switching mechanism was relatively simple, various manipulations of the reversing key and compound switch Bell Laboratories Record Courtesy www.historyofphonephreaking.org were requ tion to m, the statior to operate Switching parties w, The Co eight stat: the Paris modificati ventors in employed Betweel patents c were required by both parties to a conversation to make the necessary circuit shifts at the station, to reverse the current on the line, terns R. B. HILL ~eneral Staff ld four makes rent wHl take to operate the call bells, and to restore the switching apparatus to normal when the parties were through talking. The Connolly and McTighe system, with eight stations connected, was exhibited at the Paris Exposition in 1881, and various modifications were made in it by its inventors in subsequent patents. It was never employed in commercial service. Between 1879 and 1900, a great many patents covering dial sWitching systems tion of small exchanges, and for the most part employed complicated electromagnetic step-by-step arrangements, constantly running synchronized clockwork mechanisms, reversals of current direction, changes in current strength, and the like. None of them can be said to have advanced the automatic switching art in any practical manner, nor did any of them, so far as is known, go into commercial use. Patents Nos. 223,201 and 223,202, issued to George Westinghouse, Jr., in December, 1879, were the first to provide for the operation of a number of suburban, or satellite, rmature, a, of ,t station (b) pawl F, will het wheel G, the receiving 'lay, the telemt, letter by ier-wheel dial improvement - did not aphange patent, on September mber 9, 1879, Philadelphia; In, D. C.; and Although this :n and limited bets, it never, principle of 'tion, in addi, and call bell, pound switch, l r to that.emms, and bearcorresponding , exchange. At f were ratchet .lion, mounted umon vertical which moved by the circuit ing subscriber eif the wiper 'ontact of the ech~nisll1 was nipulations of pound switch tories Record (a) ( b) (e) Fig. I-Transmitting dial (a) and receiving dial (c) used with Froment's alphabetical telegraph system at 1851 (tram Shaffne"'s Telegraph Manual) together with the electromagnet, ratchet, and pawl arrangement used with the receiving dial (b). were isstlCd, but except for the Strowger patent (No. 447,918) of 1891 and subsequent patents pertaining to the Strowger system, nOlle resulted in a successful com- mercial system. A list of the patents falling within the Patent Office classification "Automatic Telephone Exchanges," is given in Table L Several other patents covering automatic village, house, and factory systems, not included in the above list, were also issued during this period. The twenty-six patents on· the list that were issued between the Connolly and McTighe patent of 1879 and Strowger patent No. 447,918 of 1891 all related to the opera- exchanges connected to the main manuallyoperated exchange in a city. The Village system invented by E. T. Gilliland, of the American Bell Telephone Company, and covered by patent No. 306,238, of October 7, 1884 (not included in Table I), with subsequent improvements, enjoyed a limited commercial use. It employed a number of main lines which entered all of the subscriber stations, thus eliminating the central office altogether. To make a call, a subscriber pushed in a knob corresponding to the line on which the desired station was located, which connected his telephone to that line. If, on listening, January, 1953 23 Courtesy www.historyofphonephreaking.org he found that the line was not in use, he 1892, as patent No. 481,247. This was the rang the wanted subscriber with his magneto first patent to clearly disclose the use of generator, and conversed with him. This hunks' between groups of selectors, includVillage system, which was first installed at ing the automatic selection of an idle trunk, Leicester, Mass., in' 1885, and was after- which latm· became an es'sential feature of ward employed in a number of small towns, all but the smallest dial telephone exchanges. was exhibited at the Chicago World's Fair , For the purpose of reducing the cost of giving private wire service to brokers and in 1893. In 1886, Gilliland also patented an "Auto- others who desired telegraph connection bematic Circuit Changer," patent No. 334,014, tween their offices in different cities, the whereby the operator at Worcester could inventor p!ovided only enough trunk lines pulse a rotary selector at Leicester, six miles to serve the maximum 'number of subscribaway, selecting and ringing any desired line ers who would be telegraphing at anyone of the Village system. This might be con- time. To prevent two or mare subscribers sidered an embryonic form of operator dial- from being connected to the same trunk, he ing. It was placed in actual commercial use devised a mechanism for huntiI)g for the in 1885. first trunk that was not in use. At each subForeshfdowing the complexity of later scriber station was a dial, with holes bearswitching systems was another patent, No. ing the numbers of the distant local circuits 435,295, issued to Dr. William H. Ford, of with which communication might he deSt. Louis, in August 1890. It was the result sired, and means ,for setting in motion the of several years' work by its inventor, and central office mechanism. At the, local cencontained twenty-seven sheets of drawings tral office, each subscriber line tenninated in switch, or selector, whose function was and twenty-two pages of speciRcation. Thomas D. Lockwood, manager of the to select an idle trunk. The trunk lines were American Bell Company's Patent Depart- mullipled to the bank contacts on each sement, also entered the dial switching field, lector, so that each subscriber line could and was granted two patents, Nos. 335,708 connect with every trunk. Each trunk line and 372,378, issued in 1886 and 1887, re- tel1uinated, at the distant central office, ina switch, or connector, which made the conspectively. In 1889, H. V. Hayes and H. D. Sears, of nection with the desired subscriber line. All the American Bell Telephone Company, de- of the subscriber lines at the distant central vised a dial system for small exchanges, office were multipled to the banks of all of wbich was afterward covered by patent No. the connectors. Power for actuating the 457,477, issued in 1891. It employed at the switches was supplied by a constimtly rocentral office a motor-driven rotary com- tating shaft driven by a small motor. mutating mechanism for each line, which The apparatus and method of operation could be set in motion, through a polarized of this system were far too complicated for relay and other intervening appliances, by an adequate description here. Briefly stated, plus or minus currents sen~ Qut over the line a subscriber desiring a connection inserted by the subscriber magneto generator. The a brass plug in the proper hole in his dial method of operation was quite complicated, plate, ~nd, by operating suitable hand and the system never passed the laboratory switches, caused his selector c1utch to enstage. It represented, however, the first work gage a constantly rotating disc, which ad· of American Bell engineers on true dial ex- vanced the selector brushes over the trunk terminals until the test brush encountered changes. The real advances in the dial exchange an idle trunk, whereupon the dutch was art prior to the Strowger patent of 1891 disengaged and the brush stopped. This concame from inventions not directly related nected the calling subscriber line, through to automatic telephone systems. the selected trunk, to a connector switch at On November 2, 1889, for example, J. G. the distant central office, whose brushes adSmith, of New YOrk City, applied for a patent on a dial switching system for teleIn manual switching, trunking had been emgraph lines, which was issued on August 23, ployed for many years. a (I 24 Bell Laboratories Record Courtesy www.historyofphonephreaking.org vanced over lines, one ste steps, the cal a correspond tered the bra, in a hole, wh, strength took tant connectc the desired c Although Smith patent ing principle the principl, which, in a di Bell System I In two lat 550,729, iSSUE the features I to telephone Patent No Ahearn, of C ered a watch pel a watchm at each stati, :his was the the use of 'tors, includn idle trunk, ,I featur", of Ie exchanges. ! the cost of brokers and mnection be- vanced over the terminals of the subscriber lines, one step at a time. For each of these steps, the calling subscriber dial arm made a corresponding advance until it encountered the brass plug which had been inserted in a hole,..whereupon a change in the current strength took place, which stopped the distant connector on the proper terminal, and the desired connection was completed. Although the important feature of the Smith patent was the adoption of the trunking principle, the invention also employed the principle of reverse impulse control which, in a different form, is a feature of the Bell System panel dial system. In two later patents, Nos. 550,728 and 550,729, issued in 1895, G. Smith applied the features of his dial telegraph exchange to telephone exchange operation. Patent No. 329,874, issued to Thomas It cities, the 1 trunk lines .of subscrib- g at anyone ~ subscribers me trunk, he lting for the At each sub1 holes bear- r local circuits light be demotion the he local cene terminated ventor provided at the central station a constantly rotating brush, driven by clockwork, which slowly wiped over the contacts of the lines to the various signal stations and closed the circuit of each for a definite period of time. If the watchman did not arrive at a station within the appointed time interval, he was unable to send in his signal, as the circuit through the central station indicator was destroyed. Instead, an alarm sounded at the central station. This patent was only a partial disclosure of the line finder principle, since no provision was made for stopping the rotating brush on a particular line. It is mentioned here because it was cited by the Patent Office in connection with the Van Size invention referred to below. Patent No. 393,529, issued to W. B. Van Size, of Plainfield, N. J., on November 27, 1888, and subsequently reissued, disclosed l Ahearn, of Ottawa, Canada, in 1885 , cov- an arrangement closely analogous to the line function was ered a watchman's signal. In order to compel a watchman, in making his rounds, to be at each station at the proper time, the in- finder method of operation. To simplify the equipment at a manual operator's position, and to eliminate the annunciator drop, the tlk lines were I on each se~ :r line could ,h trunk line "al office, in a ade the conriber line. All istant central mks of all of ctuating the onstantly romotor. - of operation nplicated for 3rieHy stated, ~tion inserted Ie in his dial litablehand clutch to en:c, which adver the trunk I . I a:lIl \ \ \ .I \ \ ,, I I , , .- _ _ _ _ _ JI# -- encountered , clutch was led. This conline; through ,tor switch at e brush~JS ad- ( bl tar Fig. 2-Dial arrangement (a) and switching elements (b) one subscriber's line illustrated in the Connolly OM McTighe patent of 1879. Similar switching equipment, mounted on. a common shaft E, was provided for had been em~ each line of the exchange. . aries Record .lannary, 1953 25 Courtesy www.historyofphonephreaking.org inventor provided at each position a constantly revolving radial arm or brush, connected to ground through an electromagnet and the operator's head telephone, which wiped over the circularly arranged contacts of the subscriber lines aSSigned to tbat switchboard position. When a calling subscriber operated a switch, connecting his battery to the line, it actuated the electromagnet as soon as the revolving brush reacbed his line terminal and, by means of a ratchet and pawl, stopped the brush on that terminal, thus connecting the operator's By 1900, only two general types of automatic telepbone systems had been developed, although both had various subdivisions. In the Rrst, and earliest, type, there was a direct connection of the calling and called line. Each subscriber line ended at the central office in the movable ann of an individual switch capable of making COnnection with the fixed terminals of any otber line in the exchange. All.of the subscriber lines were connected, or multipled, to the fixed terminals of each switch. Figure 3 illustrates this principle for an automatic ex- ,, ,, 7 ~~~ 1 .-'" 7 3 , " 5 5' 4 OTHER 8 5 , " 5 6' 6~ .J , '4 8~t-~ 4 6 '4 5' .L- <1- 7 , 3 5' 1 8 '2 ,3 , " 5 Fig. 3-Diagrammatic rrrresentation vi the earliest type of automatic telephone exchange. At the central ofJice there was an individual switch for each subscriber, to the wiper arm of which his line was permanently connected (center numbers). Each of the lines (eight shown in diagram) was also connected, or multipled, to its own peripheral contact on every switch. telephone into the circuit. The subscriber could then pass his call verbally to the operator, who completed it in the usual manner. Although the Van Size arrangement could hardly be called a simplification of the manual method of operation employed at that time, it did represent an interesting patent disclosure. All dial switching systems prior to the early 1890's were severely handicapped by the lack of a reliable power plant. Primary cells, such as LeClanche, Were the hest available, and the voltage va>:ied widely. 26 office trunk switches bE to one end the other el This meth cost and co paratns in Ii the use of s ity. Only el to handle 1 made at all This sec comprised there was a scrib~r line an idle trm of termina located, aI stance, thE LEADS 7 , '4 such· connE switch, COl nals of the OTHER • 5 5 • , LEADS 7 , . 5 4 OTHER 3 , 3 8.~ '2 2 6 7 3 1 5 )- 2 , 3 *4 7 7 1 ~ 1 5 7 6* .; 4 OTHER LEADS 1 8E" 2 2 5' ..<' LEADS 8·U \, The seeo exchange e fer, princi} tion betwe and called there waul change, an cuits .leadi' which mal class were stallations. In the 01 subscriber dividual' s, no such ap their lines, cuits assigi: were each ing switch, change of eight subscriber lines. For the sake of simplicity, the multiple cO,nnections to only four of the eight lines are shown. As long as the number of lines in the excbange was small - not more than one or two hundred - this type of system was practicable. In large exchanges - several thousand lines, to take an extreme case _ it is readily seen that the switches, with the necessary multiple connections, would be ptohibitive in size and cost. The Connolly and McTighe system and the early Strowger in-I stallations were examples of this type. nect with I unite those then by m, to join the terminals' finder" me played in As there ti, anism brat of lines. int minals of tl Bell Lahoratories Record January, ] Courtesy www.historyofphonephreaking.org circuit end electrical c Jes of .auto;eel) devel'us subdivitype, there calling and le ended at e arm of an naking, conof any other e subscriber pled, to the Figure S'il. ines. For the le connections es are sho~n. l1es in the ex3 than one or ;tem was prac· . several thou· ne case ,- it is , with the nee· would be proConnolly and y Strowger in· of this type. , The second, and later, type of automatic had originated a call. A path was then pro· exchange employed the trunking, or trans· vided from the calling line to an idle selector, fer, principle, in which the direct connec· which the calling subscriber could actuate : tion between the ferminals of the calling to complete his. call. Line £nders of forms . and called lines is discarded, and instead not reqUiring continuous scanning were used such connection is established through an in later Western Electric and Strowger offiCe trunk, the function of the central office Systems. switches being, first, to unite the calling line During the first twenty.five years of the to one end of an idle trunk, and then to unite telephone, up to the beginning of the twen· the other end of the trunk to the called line. tieth century, the attempts to devise a dial This method greatly diminished the first switching system had been made primarily cost and complexity of the central office ap· by inventors without practical telephone ex· paratus in large exchanges, since it permitted perience, as has already been noted. The the use of switches of relatively small capac· problem was intereSting in its ..theoretical ity. Only enough trunks had to be provided aspects, and all over the country men of an to handle the maximum number of calls inventive turn of mind and with some knowl· made at anyone tiI)Je. edge of electricity tried their hand at solving This second type of automatic system it. Some of the many bizarre proposals have comprised two distinct classes. In one class, already been described iti the Record". As a there was an individual switch for each sub· matter of fact, however, there was very little scriber line which, when operated, selected need for a dial system in these early years an idle trunk of a group leading to the bank of the telephone art. . of terminals in "{hich the called line was The objective in the minds of the many located, and then, by means of another inventors was probably to save the cost of switch, connected that trunk to the termi· operators, but for the most part they knew nals of the desired line. In Figure S, for in· too little about the telephone system and its stance, the peripheral contacts, of which requirements to realize that with an ade· there would be 100 or more for a large ex· quate dial system the saving in salaries of change, are now the terminals of trunk cir· the operators would be largely if not entirely emits leading to the switch arms of selectors offset by the greatly increased maintenance which make the final connection. In this expenses of the more elaborate switching class were included the later Strowger in· apparatus and by the carrying charges on stallations. the much greater investuJent required' The In the other class· of the second type, the real need for dial switching is due primarily subscriber lines were not provided with in· to other and much mOre complex technical dividual selecting switches, and there was and economic factors, and did not arise in no such apparatus normally connected with any appreciable intensity until well after their lines. Instead, the several trunk cir· the turn of the century. cuits assigned to a group of subscriber lines i The engineers of the Bell System had been were each provided with a suitable select· ' closely following the dial system patents ing switch, or "line finder," at their calling from the very beginning, and had carried circuit ends, adapted to seiz~ upon and can· on a little development along these lines as nect with the terminals of a calling line, to early as the late 188l1s. They recognized the unite those terminals with an idle trunk, and difficulties, however, and knew how little then by means of suitable SWitching devices would be gained from dial switching under to join the other end of the trunk with the existing conditions. There was far greater terminals of the called line. This 'nne need for developments along other IinesRnder~~ -method of operation was first" emin instruments and station apparatus, in ployed in the Lorimer and Faller systems. transmission systems and methods, and in As there nsed, a constantly 9perating mech- underground distributing systems. During anism bronght a switch common to a group the 1890's and early 1900's, for example, they of lines into successive contact with the ter- were very much occupied in developing and minals of the lines and detected the changed electrical condition produced when any line • RECORD, March, 1929, page 285. dories - Record January, 1953 utomatic ex~ ~hange, At the t which his line 'gram) WWI also 27 Courtesy www.historyofphonephreaking.org { I Table I-List of United States Patents on Automatic Telephone Exchanges Issued During the Years 1879-1900, Inclusive. * Number Date Issued PdeJitee 222,458 Dec. 9, 1879 Connolly &McTighe 113,101 Dec. 30,1879 Westinghouse, G. Jr. 223,201 bec. 30, 1879 Westinghouse, G. Jr. 224,565 Feb. 17,1880 Westinghouse, G. Jr. 237,222 Feb. 1, 1881 Westinghouse, G. Jr. 248,138 Oct. 11, 1881 BueH,C. E. 255,766 Apr. 40 1881 Buell,C. E. 262,645 Aug. 15, 1882 Connolly & Mctighe 262,646 Aug, IS, 1882 Connolly, M. D. 261,647 Aug. IS, 18B1 Connolly, M. O. 163,862 Sept. 5, 1882 Connolly, M. O. 269,130 Dec. 12, 1882 Snell, f. H. 281.613 July 17,18B3 Cardwell, G. A. 281,791 Aug. 7,1 BB3 Snell, F. H. 283,806 Aug. 28,18B3 O'Donel, I. M. . 290,730 Dec. 25, 1883 Bartelous.1. V. M. 295,356 Mar. 18,1884 • Connolly, 1. A. 310,282 Jan. 6, 1BB5 Jackson & Cole 335,708 Feb. 9,1886 Lockwood. 1. D. 349,975 Sept. 28,1886 8ickford, J. H. 349,976 Sept. 28,1886 Bickfard, J. H. 367.219 July 26, 1887 McCoy, J. A. 371,378 Nov. 1. 1887 lockwood, J. O. 381,938 May 1. 1888 McCoy, J. A. 408,327 Aug. 6, 1889 Smith, J. R. 435,295 Aug. 26, 1890 Ford, W. H. 442,734 Dec. 16, 1890 Smith & Childs 447,918 Mar. 10,1891 Strowger, A. B. 457,477 Aug. l1,1B91 Hayes & Sears 486,909 Nov. 29,1892 Strowger, A. B. 490,236 May 30, 1893 Clark, E. A. 490,189 May 30, 1B93 M,Caskey, A)S. 498,191 May 30,lB93 McCaskey, A. S. 499,748 June 20,lB93 M,Claren, A. E. 510.195 Dec. 5, 1893 Serdinko, J. 511,873 Jan. 2, 1894 Callander, R. 511,874 Jan. 2,lB94 Callender, R. 511,875 Jan. 2. 1894 Callander, R. 515,108 feb. 20, 1894 Callender, R. 515,109 feb. 20, 1894 Callender, R. 515,1 I0 feb. 20, 1894 Callender, R. 510,146 May 22, 1894 Simoneau, L. E. 518,590 Nov, 6,lB94 Childs, W. Application nate Sept. 10, 1879 Del. 11,1879 Oct. 13, 1879 Oct. 27,1879 Feb. 7, 1880 June 15,1881 Dec. 12,18Bl Aug. 29,1881 Nov. 29,1881 Nov. 8, 1881 Oct. 29, 18Bl Sept. 6, 1882 July. 7,1B82 Feb.' 28, 1883 June 5, 1880 June 15,1e82 Apr. 10,1883 Mar. 5, 1B84 Sept. 26, 1885 Nov. 25,1B85 Jan. 18, 1BB6 Jan. 29,1887 Apr. 11,1BB7 July 6, 1887 feb. 16, 18B8 Dec. 31, 1889 Sept. 27, lBB9 Mar. 12,1889 Feb. 3, 1891 feb. 19,1892 Apr. 5, 1892 July 29,1892 Aug. 25, 18n June 13, 1892 Apr. 12,1893 Apr. 14,1893 May 12, 1893 Aug. 13,1891 Nov. 2, 1893 NllV. 2,1893 Nov. 2, 1893 July 11,1893 May 12,1891 Number m,591 530,324 533,893 535,806 537,603 538,975 540,168 543,160 543,708 546,725 547,755 550,718 550,729 551.391 554,125 556,007 561,377 562,064 570,840 573,859 573,884 574,245 574,707 582.578 584,384 586,529 587,435 588,511 58Y.79B 591,201 597,062 604,373 604,434 506,764 611.974 612,6Bl 616,714 624,666 616,983 632,759 638,149 639,186 bate Issued Patentee Nov. 6, 1894 Childs, W. Dec. 4, 1894 Callender; R. Feb. 11, 1895 Hey & Parsons Mar. 12, 1895 Nissl, F. Apr. 16, 1895 Decker, W. May 7, 1895 McDonough, J. W. May 28, 1895 Keith, lundquist & Erickson July 23, 1895 Shibata, W. Y. July 3D, 1895 Shibata, W. y. Sept. 14.1895 lBerditschewsky et at. Oct. 8, 1895. Hutchins, G. K, Dec. 3, 1895 Smith, J. 6. Dec. 3, 1895 Smith. J. G. Dec. 17,1895 lounsbury, W. F. feb. 4, IB96 Hauls, W. A. Mar. 10,IB96 Freudenberg, M. June 2, 1B96 Dean, G. Q. &J. Jr. June 16, 1896 tS. Berditschewsky Brooks, M. Nov. 3, 1896 Dec. 29,1896 Callender, R. Dec, 29, 1896 Keith, A. E. Dec. 29,1896 Houts & Nilson Jan. 5, 1897 Bowm an, l. 6. May 11. 1897 Clark, Ellacott & Johnson June 15; 1897 M"kiin, A. 8. July 13, 1897 Davis, W. W. Aug. 3,1897 Freudenberg, M. Aug. 17,1897 Van Wagenen, A. Sept. 7,1897 Stmwger & Keith Oct. 5,1897 Strowger, lundqUist & Erickson Jan. 11,IB98 Keith & Erickson May 24, 1B98 'Decker, W. May 24,lB98 Stillwell &Barneck Juty 5, 1B98 Lundquist, f. ·A. ~ct. 4, 1898 Nlison, l. Go, ~tI. lJ, 1898 Snow, H. P. Dec. 27,1898 lundquist & Erickson May 9, 1899 lundquist, f. A. June 13, 1899 Decker, W. Sept. 11,1899 Slater, 1 C. pec. 5, 1899 Keith & Erickson Pec. 12,1899 Seligmann-lui. G. ., Application Date May 17,1890 Dec. 18, 1893 Mar. 30,1893 Feb. 17, 1894 May 14, 1894 May 21, 1891 Nov. 7, 1894 Oct. 11, 1894 Nov. 24, 1893 Mar. 27,lB95 May 6,1893 Feb. lB, 1893 Feb. 10, 1893 Apr. 13,1895 Dec. 24, 1894 Jan. 10, 1896 Aug. 3, 1895 MO'. 23,1896 Jan. 26, 1895 Mar. 19,1896 Sept. 16,1893 Aug. 25, 1896 July 18, 1B96 Sept. 28, 1893 Aug. 7, 1896 Sept. 5, 1896 Oct. 22, 1896 Apr. 30. 1896 Feb. 19.1896 July 17,1895 Aug. 20, 1896 Mar. 25,1895 Nov. 10,1896 May 19, lB97 Mar. 9, 1896 Nnv. 1, 1897 Mar. 28,1893 Sepl. 20,1891 Aug. 3, 1896 May 13,1898 Dec. 16, 1895 May 27. 1898 installing 1 common b, the local I had been f the telephc tuted one ever made the way fOJ phone serv much broal tricacies, b the switchi together" data to m, requiremen During t century, illl traduced 1< automatic when an OF automatic 1 answered, many othe l'eally satis! The Hrst within the with some c there was n eVen one 01 was very eJ started abol small dial E line system eration in <; follOWing y line system ~5 village, house and factory systems. t Called "Apostoloff." Not'l':-No automatic telephone exchange patenh Were issued during the year 1900, .' 28 Bell Laboratories Reco~·a Courtesy www.historyofphonephreaking.org J annary, '1.9: installing throughout the Bell System the . and 100-line capacity, were built during common battery system to take the place of 1904 and 1905, to a total of more than 40. the local battery or magneto system that Experience indicated,. however, that the had been employed since the beginning of operation of dial switching equipment in the telephone- business. This system consti- unattended offices brought in additional retuted one of the most important ,advances quirements that were difficult if not imposever made in the telephone art, and opened sible to meet at that time, As a result, these the way for a tremendous expansion in tele- installations were later reconverted to manphone service. It also gave the engineers a ual operation. It was not until many years much broader and clearer picture orthe In- later that dial switching for small unattricacies" bdth technical. and economic, of tended offices proved technically and ecothe switching problem in large exchanges, nomically practicable. together with all of the necessary traffic At about this same, time, however, it bedata to make intelligent plans for future gan to become evident that beforejhany reql.;lir'ements. years dial switching would be needed to During the later years of the nineteenth meet the complex conditions in the larger century, moreover, many features were in- cities, where it was foreseen that there would troduced to save operating effort, such as not be a sufficient number of competent automatic ringing of a called subscriber operators available to do all switching manwhen an operator plugged into his jack, and ually. As a result, the development of dial automatic tripping of the ringing when he switching within the Bell System had exanswered. All, of these developments and panded into an intensive program by 1905. many others were paving the way for a It resulted in the trial of a semi-automatic really satisfactory dial system. system at West Street in 1910, ill the comThe first real need for dial operation mercial installation of a semi-automatic within the Bell System arose in connection panel system in Newark in 1915 and later in with some of the smaller',communities where the full automatic panel dial system. there was not a full time operating load for Although many patents had been issued even one operator, and thus 24-hour service on dial switching systems prior to the Bell was very expensive. Work was accordingly System work beginning about 1900, and started about 1900 on the development of a most of the elementary switching principles small dial exchange, and during 1902 a 50- had been disclosed, none of the systems that :xchanges Application nate May 27, ~". 18,1893 Mar. 30.1ai3 feb. 17.1894 May 14, 1894 May 21. 1891 Nov. 7. 1894 ErickslHl Oct. 11,1894 Nov. 24.1893 Mar. 27,1895 al, May 6, 1893 feb. 18.1893 feb. 20. 1893 Apr. 23,1895 D". 24.1894 Jan. 10. 1896 Aug. 3. 1895 r. Mar. 23.1896 Jan~ 26. 1895 Mar. 19,1896 Sept. 16. 1893 Aug. 25, 1896 July 18, 1896 Sept. 28. 1893 Johnson . Aug. J. 1896 Sepl. 5, 1896 Od. 22,1896 Apr. 30, 1896 feb. 19.1896 ist & Erickson July 17,1895 Aug. 20.1896 Mar. 25,1895 Nov. 10,1096 :k May 19.1897 Mar. 9, 1896 Nov. 1,1897 Mar. 28,1893 :50n Sept. 20, 1897 Aug. 3, 1896 May 23, 1898 nee. 15. 1095 May 27,1898 rere issued during the year 1900. line system was placep. In ,experimental op- were devised enjoyed any extensive com- eration in Queens, Long .Island, During the following year this was replaced. by a 100line system. Other such systems, of 20-line mercial use except that of Almon B. Strowger and his associates. This latter system will be the subject of a forthcoming article. THE AUTHOR: ROG~" B. HILL received a B.S. degree from Harvard University in 1911 and entered the Engineering Deparhnent of the Ameri- can Telephone and Telegraph Company in August of that year. For several years thereafter he was engaged principally in appraisal and depreciation studies. When the Department of Development and Research was fanned in 1919, he transferred to it, and since then, until his retirement in 1951, had been largely concerned with studies of the economic phases of development and operation. He had been a member of the staff of Bell Telephone Laboratories since 1934, Brst in the Outside Plant Development Department and later in the Staff Department. In addition to his work on the economic side of the telephone businer3, Mr. Hill exhibited a great interest in the early history of [1 the telephone art, and assisted with the preparation of several books and articles dealing with that subject. aries Record, .J anuary, 1953 29 Courtesy www.historyofphonephreaking.org