Prof. H. Hennessy on the Figures of the Planets. 283 



Acid containing 0*192 gramme per 100 cubic centime. — Kohl- 

 rausch and Nippoldt found that the resistance of acid of 0*2 

 per cent. H 2 S0 4 was 465100 times that of mercury at 22°, 

 whence the specific resistance of acid of -192 gramme per 100 

 cubic centims. may be taken as close to 45 ohms ; so that with 



the voltameter used R=— — — = 245 ohms, the plates being 



6 centimetres apart, and the bore of the tube between them 

 averaging l'l square centimetre in section. The surface of 

 each electrode with this voltameter was 3*5 square centi- 

 metres. 





iMicrowebers per. 





| 





Current. 



| square centi- 

 metre. 



E. 



CR. 



e=E-CR. 



4-6 



1-31 



2186 



•001 



2-185 



15-2 



4-34 



2-300 



•004 



2-296 



31-7 



9-1 



2-363 



•008 



2-351 



603 



17-2 



2-468 



•015 



2-453 



100-9 



28-8 



2-542 



■025 



2-517 



Fig. 4 represents the curves obtained with these different 

 strengths of acid, the abscissas being in each case the current- 

 flow per square centimetre of electrode surface : curve no. 1 

 is that obtained with acid of 40-0 grammes per 100 cubic 

 centims. ; the curve marked no. 2, that with acid of 11*4 

 grammes ; those marked 3a and 3b the two with acid of l'O 

 gramme per 100 cubic centims., obtained respectively with 

 voltameters no. 2 and no 1 ; the curve marked 4 is that with 

 acid of 0*192 gramme per 100 cubic centims. ; whilst curve 

 no. 5 is the average curve deduced for acid of 27*0 grammes 

 per 100 cubic centims. from the preceding four sets of ex- 

 periments. In all cases, the weaker the acid the greater is the 

 counter EiM.F. set up with a given rate of flow of electricity 

 per unit area of electrode surface. 



[To be continued.] 



XXXVII. On the Figures of the Planets. By Henry Hen- 

 nessy, F.R.S., Professor of Applied Mathematics in the 

 Boyal College of Science, Dublin *. 



N the Comptes Rendus for June 14, 1880, I gave, for the 

 compression of a planet from the action of superficial 



I 



abrasion, the formula 



5QD 



e = 



2(5D-3)-6(D / -l)' 



* Translated from the Comptes Rendus of the Paris Academy of 

 Sciences for January 31, 1881, p. 225. 



