40 President's Address. . [Feb. 



representative, as closely as 3 per cent. Kohlrausch proposes that the 

 Siemens unit should be introduced as the material standard for reference, 

 especially as the Siemens unit is capable of such accurate reproduction, 

 as has been shewn by different observers at different times, the error of 

 reproduction of the Siemens unit exceeding scarcely half per mille. This 

 material standard might then be expressed from time to time in absolute 

 measure for scientific purposes. Its value would then be known more and 

 more accurately in absolute measure in proportion as the methods of deter- 

 mination increase in accuracy, and by this proceeding endless confusion in 

 future might be avoided. 



Mr. Siemens when proposing his unit had foreseen most clearly all these 

 difficulties connected with the production of a standard in absolute measure. 

 Further his unit being so easily understood and having already attained such 

 a wide extension in all electrical measurements. Professor Kohlrausch's 

 proposals are very much to the point. 



JElectromotograpJis. — Another, and entirely new, discovery in Telegra- 

 phy has been made during the last year by Mr. T. A. Edison, of Newark. 



The instrument is based on the newly discovered fact that when an 

 electric current, even the weakest which would not be able to deflect even a 

 very delicately suspended magnetic needle, passes through paper prepared in 

 the ordinary manner as is used for the chemical telegraphs, the surface 

 becomes changed, i, e., where the current has passed, it becomes smooth, while 

 in the other parts, where no current has passed, the paper keeps its original 

 surface. This is the case, as already stated for the weakest possible currents, 

 which would not even be able to produce coloration by electrolysis. Thus 

 if a lever is introduced in the proper manner and is made to pass over 

 these unreadable signals, the lever slides upon the paper, as upon ice when 

 passing over a signal, but when no signal is under it, the lever is carried 

 forward by the friction of the paper producing a certain motion of the lever 

 which by the application of local batteries is made to reproduce the message 

 in a readable manner. 



It will be clear that no electro-magnets being used, the speed of receiv- 

 ing a message is only limited by the induction capacity of the line and by 

 nothing else, and moreover the weakest possible currents being sufficient to 

 produce this peculiar state of the paper, such a telegraph will work when all 

 the present known ones would cease to function. 



Mr. Edison finds that paper prepared with potassic hydrate is the 

 best material for producing the required effect on the paper. This system 

 in continuation with the now perfectly practicable Duplex working will raise 

 the carrying capacity of the telegraph line to such an enormous extent that 

 we may well expect to defer indefinitely the construction of new lines where 

 old ones do already exist. 



