DISCOURSE OF W. B. TAYLOR. 263 



example even by a fog or precipitation of vapor at one station) as 

 also from induction at a distance, the danger to travellers along a 

 telegraph road would be very slight, unless a person should be 

 standing or passing quite close to a pole at the moment of its being 

 struck. He however recommended that for the protection of the 

 poles, they should be provided with conductors. "The effects of 

 powerful discharges from the clouds may be prevented in a great 

 degree by erecting at intervals along the line and beside the support- 

 ing poles a metallic wire connected with the earth at the lower end, 

 and terminating above at the distance of about half an inch from the 

 wire of the telegraph. By this arrangement, the insulation of the 

 . conductor will not be interfered with, while the greater portion of 

 the charge will be drawn off. I 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 discharge falling on the wire near the station might send a 

 current into the house of sufficient quantity to produce serious acci- 

 dents." * This precaution has now been largely adopted, especially 

 on the telegraph lines of the central portion of the United States, 

 which are more liable to the effects of lightning, f 



Molecular Physics. Among other inquiries many original exam- 

 inations 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 capillarity. 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 exam- 

 ination 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. 



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



fPrescott. Electricity and the Electric Telegraph, 8vo. N. York, 1877, chap, xxiii. 

 pp. 296 and 411. 



