1839] WRITINGS OF JOSEPH HENRY. 147 



substituted for the one before described, the globule of mer- 

 cury did not make its appearance at the lower end until 

 about forty days, and all the mercury of the upper glass 

 had not yet (after three months) entirely disappeared. 



The penetration takes place much more readily in the 

 direction of the laminse of the metal than across them. A 

 plate of thick sheet lead was formed into a cup, and mercury 

 poured into this; and it was found that before a drop had 

 passed directly through, the mercury oozed out all around 

 the edge of the plate. 



Professor Henry stated that he had in progress a variety 

 of experiments to investigate this action, and if any results 

 of importance were obtained he would communicate them 

 to the Society. 



LETTER ON ELECTRICAL INDUCTION. 



(Proceedings of the American Philosophical Society, vol. i, pp. 134-136.) 

 October 18, 1839. 



The following extract from a letter addressed by Professor 

 Henry to Professor Bache was read, announcing the discov- 

 ery of two distinct kinds of dynamic induction by a gal- 

 vanic current. 



" Since the publication of my last paper, I have received 

 through the kindness of Dr. Faraday a copy of his four- 

 teenth series of experimental researches, and in this I was 

 surprised to find a statement directly in opposition to one of 

 the principal results given in my paper. It is stated in 

 substance in the 59th paragraph of my last communication 

 to the American Philosophical Society, that when a plate of 

 metal is interposed between a galvanic current and a con- 

 ductor the secondary shock is neutralized. Dr. Faraday 

 finds, on the contrary, under apparently the same circum- 

 stances, that no effect is produced by the interposition of 

 the metal. As the fact meritiontd forms a very important 

 part of my paper, and is connected with nearly all the phe- 

 nomena described subsequently to it, I was anxious to in- 

 vestigate the cause of the discrepancy between the results 

 obtained by Dr. Faraday, and those found by myself. My 



