354 Direct Solution of a Geometrical Problem. 



found to be = 1*0473. Owing to an injury to the unit, the com- 

 parison had to be made in the air ; and therefore no great weight 

 must be assigned to it. The British-Association units belonging 

 to M. Brix (No. 21) and M. Weber (No. 51) were also compared, 

 and gave, in accordance with the above, the value 1*0493. If 

 this agreement be compared with the former enormous differ- 

 ences in the statements regarding units of resistance, a very- 

 satisfactory proof is afforded as to the progress in this kind of 

 measurement*. 



Taking the number 1*0493, it will be found that this unit is 

 nearly 2 per cent, more than was intended. 



The electromotive forces of Daniell and Grove I have found, in 

 conjunction with Ammann, to be =11*71 and 19*98 Siemens- 

 Weber units respectively; they have therefore the absolute 

 value f 



-n -n -II oo inin millim.t milligrm.i 



Daniell = 11*38 x 10 10 -^P • 



second' 2 



Grove = 19*42 x 10 10 



The thermoelectric force of German-silver-iron, expressed in 

 the same units, =2400000 for a difference in the junctions of 

 one degree at mean temperatures. 



XLIII. Direct Solution of a Geometrical Problem. 

 To the Editors of the Philosophical Magazine and Journal. 



Gonville and Caius College, 

 GENTLEMEN, Cambridge, March 2/, 1874. 



MAY I request the publication in your Magazine of the 

 accompanying paper and letter which came from a 

 lady in California? The paper, as you will see, is a solution 

 of a geometrical problem which, more than twenty years ago, 

 excited considerable interest by its discussion in your Magazine. 

 The Vice- Chancellor of Cambridge, to whom these documents 

 were addressed, placed them in my hands ; and at his request I 

 forwarded them to Professor Sylvester, who expresses the opinion, 

 with which I entirely agree, that the solution is thoroughly 

 sound, and authorizes me to say that he has suggested the pro- 

 priety of the publication of the papers in your Magazine. In 

 this suggestion the Vice-Chancellor cordially concurs. . 

 I am, Gentlemen, 



Your obedient Servant, 



N. M. Ferrers. 



* The research will be found in Poggendorff's Annalen, vol. cxlvii. p. 155. 



t Compare Pogg. Ann. vol. cxli. p. 458, wherewith it must be remarked 

 that, after the necessary reductions, the numbers which Ammann and I 

 have found agree very closely with the results of Waltenhoftn (Pogg. Ann. 

 vol. cxxxiii. p. 478). " 



