338 



SECENT PROGRESS IN PHYSICS. 



In the last column the deflections of the compass needle produced by 

 the magnetized needle are indicated as explained above. Where no i 

 deviation is indicated the magnetism was not perceptible. 



As far as the last three observations, indicated -by *, the observed 

 temperatures harmonize very well with the formula 



s 



From all the observations (the tables given by Kiess contain a few v 

 more) the mean result for a was 0.075 ; the temperatures computed 

 with this co-ef&cient in the' above formula accord perfectly well with 

 the observed values. Hence the formula holds good for the tempera- 1 

 tures produced by the secondary current. 



In the observations indicated by * the secondary circuit was inter- r 

 rupted, so that the current had to pass with a spark. This has a 

 very important influence (above mentioned) upon the magnetization, i 

 It is shown here, while the heating power is scarcely afiected — it being i 

 a little diminished. 



When a Glerman silver wire, 78 lines long and half a line thick, was i 

 inserted in the main circuit the heating was less ; the co-efficient a, 

 which was found above equal to 0.075, was now 0.028. 



As may be readily conceived, the quantity of electricity in the 

 secondary current is greater in proj^ortion as the portion of the main 

 spiral acting upon the lateral spiral is greater, other circumstances 

 being equal. In order to determine the amount of increase of the 

 secondary current thus produced, the secondary coil B B, (fig. 59,) 

 closed by the platinum wire of the thermometer, was slipped over the 

 straight prolongation of A A, and the temperature noted which was 

 produced in the secondary wire by the discharge of g = 20 in s = 5. 

 Then, in successive experiments, a different number of coils of the 

 main spiral was brought under the secondary spiral, and the same 

 quantity of electrifity discharged in the same manner. These experi- 

 ments gave the following results : 



The numbers of the last column are the mean of two series of ex- 

 periments, giving nearly the same results. 



Since we know what elevation of temperature (1.85) is produced in 

 the secondary v/ire by the action of a straight piece of the main wire 

 134 lines long, we can compute the heat produced by the action of a 

 straight piece of the main wire 102, 634, &c., lines long, and thus 



