276 BULLETIN OF THE 



arrangement, the insulation of the conductor will not be inter- 

 fered with, while the greater portion of the charge will be drawn 

 off. 1 think this precaution of great importance at places where 

 the line crosses a river and is supported on high poles. Also in 

 the vicinity of the office of the telegraph, where a dischage fall- 

 ing on the wire near the station might send a current into the 

 house of sufficient quantity to produce serious accidents."* This 

 precaution has now been largely adopted, especially on the tele- 

 grapli lines of the central portion of the United States, which are 

 more liable to the effects of lightning. f 



Moleculai- Physics. — Among other inquiries many original 

 examinations were made by Henry in the domain of molecular 

 physics. While Professor in the College of New Jersey in 1839, 

 his attention was attracted to a curious case of metallic capil- 

 larity. A small lead tube about eight inches long happening to 

 be left with a bent end lying in a shallow dish of mercury, he 

 noticed a few days afterward that the mercury had disappeared 

 from the dish, and was spread on the shelf about the other end 

 of the tube. On a careful examination of the tube by incision, 

 it appeared that the mercury had not passed along the open canal 

 of the tube, but had percolated through its solid substance. To 

 test this, a solid rod of lead about one-fourth of an inch thick 

 and seven inches long was bent into a siphon form, and the 

 shorter end immersed in a small shallow vessel of mercury; a 

 similar empty vessel being placed under the longer end. In the 

 course of 24 hours a globule of mercury was found at the lower 

 end of the lead rod; and in five or six days it had all passed 

 over excepting what appeared in the form of crystals of a lead 

 amalgam in the upper vessel. J A long piece of thick lead wire 

 was afterward suspended in a vertical position, with its lower 

 end dipping into a cup of mercury. In the course of a few days, 

 traces of the mercury were found in the rod at the height of 

 three feet above the cup : thus showing that a metal impervious 

 to water or oil (excepting under very great pressure) was easily 

 penetrated to great distances by a liquid metal. 



Some years later on a visit to Philadelphia he endeavored with 

 the assistance of his friend Dr. Patterson (then Director of the 

 United States Mint), by melting a small globule of gold on a 

 plate of clean sheet-iron, to obtain its capillary absorption ; but 

 without effect ; probably owing to the interposition of a thin film 

 of oxide. Applying to another personal friend, Mr. Cornelius 

 of Philadelphia, a very intelligent and ingenious manufacturer 

 of bronzes, and plated ornaments for chandeliers, etc. to try 



* Proceed. Am. Phil. Soc, vol. iv. p, 266. 



t Prescntt. Elertncih/ and the Electric Telegraph, 8vo. N. York, 1877^ 

 chap, xxiii. pp. 296. and 411. 



t Proceed. Am. Phil. Soc., vol. i. p. 82. 



50 



