2-14 Prof. Hare on a Single-leaf Electrometer, $c. 



tion, combined with those which you have made of the inca- 

 pacity of the deflagrator, and Voltaic series in the usual form, 

 to act when in combination with each other, must justify us 

 in considering the former as a galvanic instrument having 

 great and peculiar powers. 



Since the above was written, I have tried my series of 300 

 pairs. The projectile power and the shock were proportion- 

 ally great, but the deflagrating power was not increased in 

 proportion. The light was so intense that, falling on some 

 adjacent buildings, it had the appearance of sunshine. — Having 

 had another series of 300 pairs made for Dr. Macnevin of 

 New York, on trying it I connected it with mine, both col- 

 laterally and consecutively, so as to make in the one case a 

 series of six hundred, in the other a series half that in num- 

 ber, but equal in extent of surfaces. The shock of the two, 

 consecutively, was apparently doubly as severe as the shock 

 produced by one ; but the other phenomena seemed to me 

 nearly equally brilliant in either way. 



The white globules which you noticed were formed copi- 

 ously on the ignited plumbago, especially in vacuo. I have 

 not had leisure to test them, being arduously occupied in my 

 course of lectures, and in some efforts to improve the means 

 of experimental illustration. 



Account of an Electrometer, tvith a single Leaf, by which the 

 Electricity excited by the Touch of heterogeneous Metals is 

 rendered obvious after a single Contact. 



Fig. 7 represents an electrometer, with a single leaf sus- 

 pended from a disk of zinc six inches in diameter, which con- 

 stitutes the top of the instrument. Opposite to this single leaf 

 is a ball supported on a wire, which may be made to approach 

 the leaf; or recede from it, by means of a screw. Above the 

 instrument is seen a disk of copper with a glass handle*. 

 The electricity produced by the contact of copper and zinc, is 

 rendered sensible in the following manner. Place the disk of 

 copper on the disk of zinc (which forms the canopy of the 

 electrometer) : take the micrometer screw in one hand, touch 

 the copper disk with the other, and then lift this disk from the 

 zinc. As soon as the separation is effected, the gold leaf will 

 strike the ball, usually, if the one be not more than T ^„ of an 

 inch, apart from the other f. Ten contacts of the same disks, 

 of copper and zinc, will be found necessary to produce a sen- 



* For the experiment with this electrometer a metallic handle would 

 answer. Its being of g.ass enabled me to compare the indication thus ob- 

 tained with that obtained by a condenser. 



f I have seen it strike at nearly double this distance. 



sible 





