Improvements in Science. 



291 



M' (T" — r') + m! c ( t' — r') = m' \, 

 or, M = fi ml 



/x (T" —t') + c (f — r') = X. 



And in the last case 



/x (T" — r') + c (f — r") = X- 

 Eliminating X from these two equations, we obtain the 

 value of c, or the specific heat of the salt. 

 The following are the results : 



Solutions of Common Salt. 



Experiment. 



Salt in 

 100 water 



7-75 

 7-705 

 13-195 

 12-983 

 31-711 

 31-172 

 15-427 

 15-372 



Calculation gives the following values for c and X. 



Salt in 



100 parts 



water 



7-740 0-1725 15-002 



13-089 0-1744 12-776 



15-400 0-1781 11-483 



31-441 0-1732 6-867 



The mean value of c is = 0-1743. The value of X changes 



with the quantity of salt. When the solution of the salt 



contains no more than 4 per cent, of salt, the value of X = 



16*8. With a maximum of salt, its value appears to be = 



3-4. With a minimum = 18-6. 



With a solution of sulphate of magnesia, the mean value 

 of c was found to be = 0*2906 and X a constant quantity.* 



Temperature at different depths. — M. Quetelet has pub- 

 lished some observations, which he has made at Brussels, 

 in reference to the temperature at different depths. At a 

 depth of 17 centimetres (6*18 inches), the mean temperature 

 of the year 1834 was 51°; at 55 centimetres (2T6 inches), 

 the mean temperature was 51°| ; at 75 centimetres (29-47 

 inches), the temperature was 52°- 19 ; at 1 metre (3*28 feet), 

 52-95. — (Correspondance Mathem. et Phys., viii. 303.) 



* Poggendorff 's Ann. xxxv. 



u 2 



