1875.] ^4:0 [Barker. 



6. Two cubes of boiling water acted differentially on the pile. At the 

 distance of five centimeters, the deliectioa was 20° ; moving one to ten 

 centimeters, the deflection was reduced to 5°. 



7. Voltaic current. — A. drop of water was placed on a zinc plate. 

 While one of the connecting copper wires touched the zinc, the other was 

 made to totich the water. The deflection was 16°. 



The claim which is here made for the instrument however, is rather for 

 the general principle of its construction, than for the advantages possessed 

 by the individual galvanometer above described which was constructed at 

 short notice, to meet an emergency. The comparatively small cost for 

 which it may be fitted to the vertical lantern, the readiness with which it 

 may be brought into use, the bi'illiantly illuminated circle of light which 

 it gives upon the screen, with its graduated circle and needle, the great 

 range of delicacy which may be given to the instrument by varying the 

 coil and needles, so. that all experimental requirements may be answered, 

 and finally, the satisfactory character of its performance as a demonstra- 

 tion galvanometer, all combine to jvistify the record which is here made 

 of it. 



PMladelpMa, April, 1875. 



