298 SEC. 10. ELECTRICITY. 



15O4g. Clark's Standard Element. 



Warden, Muirhead, and Clark. 



X.STANDARDS OF COMPARISON FOR MEASURE- 

 MENT OF ELECTRICAL MAGNITUDES. 



1505. Weber's Resistance Coils, No. 3 and No. 5, certifi- 

 cated to represent the following resistances : 



No. 3=60717 x 10 5 Weber's absolute units. 



No. 5=59440xl0 5 - 



T. Bosschtty Professor, Royal Polytechnic School, Delft. 



Comparisons of these coils were published by Dr. Schroder van der Kolk 

 in Poggendorff's Annalen, vol. 110, p. 465. 



The coil No. 3 was used in the first determination of the electro-motive 

 force of a Daniell's cell in absolute measure, executed in 1857 by Dr. Bosscha. 

 This electro-motive force was found to be 1026 x 10 8 metres absolute units. 

 Applying Sir William Thomson's theorem (Phil. Mag., Series IV., vol. ii. 

 p. 557), the mechanical equivalent of heat derived from this result is 432' 1 as 

 compared with MM. Favre and Silbermann's determination of the heat gene- 

 rated by the action of zinc on sulphate of copper; 419*5 as compared with 

 Mr. Joule's experiments on the heating power of a Daniell's cell (Phil. Mag., 

 Series IV., vol. iii.), discussed in Poggendorff's Annalen, vol. 103 ; 437 '3 as 

 compared with similar experiments of Professor Lenz (Pogg. Ann., vol. 59, 

 p. 203), discussed in Poggendorff's Annalen, vol. 108, p. 162 ; and 421-1 as 

 compared with similar experiments of Mr. Joule, related in " Memoirs of the 

 " Lit. and Phil. Soc. at Manchester/' vol. vii. p. 94, and discussed in Poggen- 

 dorff's Annalen, vol. 108, p. 168. 



1506. Siemens 9 Resistance-Unit. 



Siemens and Halske, Berlin. 



1506a. Normal Mercury Unit in glass spiral. 



Siemens and Halske, Berlin. 



1507. Conductivity Apparatus, for comparing the conduc- 

 tivity of wires of copper, or any other metal or alloy, with 100 

 inches of pure -copper weighing 100 grains, 200 inches weighing 

 100 grains, or 300 inches weighing 100 grains. The conductivity 

 is determined by resistance, length, and weight. 



Elliott Brothers. 



XI. APPARATUS FOR THE APPLICATION OF 

 ELECTRICAL PRINCIPLES TO PRACTICAL PURPOSES. 



a. TELEGRAPHIC APPARATUS. 



1508. Two Drawings of plans, sections, and elevations of 

 machinery of Sir C. Wheatstone's proposed scheme for a sub- 

 marine telegraph cable, 1840. Robert Sabine, Regent's Park. 



