300 SCIENTIFIC APPARATUS. 



thermometers intended for taking the temperature of the rock 

 and of water may be cited. Of the former, beyond their being of 

 sufficient length, accurately divided, and left for an ample time 

 plugged up in a bore-hole prepared a day or two beforehand, 

 there is perhaps not much to be observed ; but when we come to 

 the more debatable ground of deducing the temperature of the 

 rock from observations in deep shafts or bore-holes full of water, 

 the nature of the instrument to be used will require much 

 discussion. 



Some of the most notable results of this kind obtained of late 

 years have been those of M. Walferdin, at the bore-hole of 

 Mouille-longe, near Creuzot, and those noted in the unrivalled 

 deep-boring by the Prussian Government, at Sperenberg, near 

 Berlin. In the first of these the maximum thermometer of M. 

 Walferdin was employed, as described in Pouillet's Physique, 

 Paris, 1856, but the observations appear not to have been car- 

 ried on to the extreme depth of the bore-hole. Those at Speren- 

 berg were made with thermometers on a principle proposed by 

 Magnus,* and constructed by Apel, of Gottingen. In spite of all 

 precautions, some curious anomalies appear among the results, 

 and when we find, in the last instance, a temperature of 118*6 

 Fahr. at the depth of 4,042 feet, it is only a wonder, considering 

 the ascending and descending currents that are set up in the 

 column of water, that anything so near to a regular scale of incre- 

 ment of heat has been obtained. 



ELECTRIC EXPLODERS FOR FIRING SHOTS. 



The employment of electricity is as yet somewhat rare among 

 civil miners, although there are, doubtless, many conditions under 

 which it would be desirable to introduce so safe a method of 

 firing charges, especially if they are large or numerous. The 

 battery, the ebonite electric disc, and the magneto-electric 

 machine, with the various fuzes for firing the shot, will form a 

 * See Pogg. Ann., vols. 98 and 116. 



