208 



Dr. C. W. Siemens. 



[Mar. 4, 



quarter of an hour, to the highest heat (about 1,700° C.) of a Siemens 

 regenerative furnace, two platinum crucibles, one filled with powder 

 residue, the other with potassium hyposulphite. At the conclusion of 

 the exposure, and while the crucibles were still red hot, they were 

 plunged into water, deprived of air by long-continued boiling, and at 

 once sealed. The powder residue was found still to contain 1*27 per 

 cent, of hyposulphite, while the crucible with the pure salt consisted 

 of a mixture of sulphate and sulphide, but with an amount of 2'1 per 

 cent, of hyposulphite. 



It is probable that, if the exposure had been still longer continued, 

 the hyposulphite would have altogether disappeared, and the experi- 

 ment can only be taken as proving that the hyposulphite, especially if 

 mixed with other salts, is neither quickly nor readily decomposed, 

 even at very high temperatures. 



II. " On the Dynamo-Electric Current and on certain Means to 

 Improve its Steadiness." By C. AViLLiAM Siemens, D.C.L., 

 LL.D., F.R.S. Received March 1, 1880. 



(Abstract.) 



The author, after alluding to the early conception by Dr. Werner 

 Siemens of the dynamo-electric or accumulative principle of generating 

 currents, makes reference to the two papers on the subject presented, 

 the one by Sir Charles Wheatstone and the other by himself, to the 

 Royal Society in February, 1867. The machine then designed by 

 him, and shown in operation on that occasion, is again brought 

 forward with a view of indicating the progress that has since taken 

 place in the construction of dynamo- electrical machines, particularly 

 those by Gramme and Siemens-von Alteneck. The paper next points- 

 out certain drawbacks to the use of these machines, both of them 

 being subject to the disadvantage that an increase of external resist- 

 ance causes a falling off of the current ; and that, on the other hand, 

 the short circuiting of the outer resistance, through contact between 

 the carbon electrodes of an electric lamp, very much increases the 

 electric excitement of the machine, and the power necessary to main- 

 tain its motion, giving rise to rapid heating and destructive sparks in 

 the machine itself. 



An observation in Sir Charles Wheatstone's paper is referred to, 

 pointing to the fact that a powerful current is set up in the shunt 

 circuit of a dynamo-electric machine, which circumstance has since 

 been taken advantage of to some extent by Mr. Ladd and Mr. Brush, 

 in constructing current generators. 



The principal object of the paper is to establish the conditions under 



