TRANSACTIONS OF SECTION A. 617 



about 400 pages now in the press at Messrs. Clowes & Sons', Ld., containing 

 nearly all that has been published relating to the calculating machines of Charles 

 Babbage. 



The paper sketches the origin of the engine in 1833-4 and describes the chief 

 means employed to direct it. 1st. The cards which have been already more or less 

 described. 2nd. The principle of ' chain,' by which any possible contingency 

 among many may be provided for. There is a movable block for each event 

 anticipated, which on the occurrence of the event is moved into a certain position ; 

 a lever or arm is made to act, so that when the movable block is in that position 

 it is moved and passes on the motion to something else, effecting whatever change 

 may be desired in the mechanism. If the block is not in that position, the lever 

 moves in vain. This arrangement is applicable to one or to many events. The 

 shape of the block may be varied to suit different purposes. This principle is used 

 to put various parts of the engine into and out of gear automatically. It is also 

 used in anticipating carriage, which is described at some length, showing how by 

 the use of ' chain ' every possible case of carriage in n figures maj' be mastered and 

 the whole effected simultaneously, the mechanism indeed presenting to the eye a 

 sort of picture of each combination as it occurs. A double camb is explained, 

 which is extensively used for producing intermittent motion required at fixed 

 times. 



The frequent use of c junting apparatus of sorts for recording and regulating 

 the various trains of motion is mentioned, and the advisability of making these 

 trains as short as possible and taking a fresh start from the motive power is urged. 

 Various other details are more or less alluded to or discussed. 



The notations and drawings (of which there is a full list in the forthcoming 

 volume) are mentioned, and the system of' meclianical notation ' used by the inventor 

 (see Proceedings of B. A. for 1855 at Glasgow) is mentioned ; an instance of its 

 practical utility is given, and its being taught in art and technical schools is 

 recommended. 



As regards the report of the Committee presented to the B. A. in 1878, it is 

 urged that the powers of the analytical engine are not limited to the production 

 of a 'single numerical result,' but can follow the matliematician wherever he can 

 point the way, and that its processes (including division) are not tentative except 

 so far as the mathematician makes them. Some further objections are made to 

 certain points in the report, which, considering the improbability of the engine 

 ever being constructed, may be here passed over. It is admitted that the scope 

 and powers of the design may be very considerably restricted, with the result of 

 leaving a machine which would still be excessively useful and which woidd 

 inevitably lead the way to further progress. 



It may here be stated that a pieceof machinery working to 29 places of figures, 

 and embodying the anticipating carriage, was shown during the meeting to several 

 who desired to see it. The anticipating carriage works perfectly, and was much 

 admired by those who saw it. 



4. On a Modification of MaxweWs Equations of Electromagnetic Waves, 

 By Professor H. A. Rowland. 



6. On a Photographic Image of an Electric Arc Lamp, prohahjy due to 

 Phosphorescence in the Eye, and on some Photographs of an Eclipse of 

 the Moon. By Fpjese Greene. 



The eye was exposed to a 2,000 candle lamp, the current was switched off, and 

 a sensitive plate was immediately held before the eye. Some of the plates after- 

 wards showed a minute picture of the glowing carbons. 



Photographs of the moon were also exhibited which had been taken by what 

 was practically a Newtonian telescope without a lens. 



