162 Prof, Backers Report on the U. S. Coast Survey. 



work. In this wise, the appropriation for the Survey is made, 

 while effecting its own end, to contribute to the maintenance and 

 encouragement of a class devoted to science — and who may per- 

 haps thus be assisted to repay their country in future fame, as 

 well as in present labor. 



In addition to the employment alluded to of telegraphic con- 

 nections for determination of differences of longitude, researches 

 have been prosecuted on the velocity of the galvanic- current. A 

 measurable interval having appeared in the recording of signals 

 at different points, experiments were instituted, connecting the 

 Washington station with Cambridge, Mass., St. Louis, and 

 Charleston, S. C, under various circumstances. The. results indi- 

 cate a velocity of about 15,400 miles per second, by the iron 

 wires, while it appears probable that, in passing through the 

 ground^, the wave has not a velocity exceeding two-thirds of 

 the former. In the course of these experiments, interesting phe- 

 nomena have been noticed, indicating apparent crossing and inter- 

 ference of the galvanic waves departing from the two poles of the 

 telegraphic circuit. 



Under an arrangement for ascertaining differences of longitude 

 from Europe, by the transportation of chronometers, one series 

 of results has been completed, and another is commencitig. Mr. 

 Bond, Director of the Cambridge Observatory, who had the im- 

 mediate charge of the matter, states the very curious fact that 



the eastern passages giv^e a greater difierence of longitude than 



the western — and this too uniformly to be the result of accidental 

 errors of the chronometers. 



In the conduct of the Survev, it has been difScult to ascertam 

 the best season for its various operations on different parts of the 

 coast, the most pleasant weather not being always the most suit- 

 able, especially when the lines of sight are long. In the Florida 

 section experience indicates the months from November to June 

 (embracing parts of each, and including the intermediate months 

 except March) as best for triangulation ; and the same months, 

 substituting March for June, as best for topography. 



At the office of the Survey, the reproduction of engraved plates 

 by the electrotype process has been pursued with complete suc- 

 cess. The method consists in washing the plate with an alco- 

 holic solution of iodine, and exposing to the action of a strong 



light, before placing it on the battery. In replacing a destroyed 

 plate, the practicability has been proved of cutting up plates in 

 the engraving, distributing the parts to several engravers, and re- 

 producing the whole in one plate. The mode adopted was to 

 secure the parts by screws to a copper plate and, fill in with cop- 

 per filings the intermediate spaces, made exceedingly small by 

 close filing of the edges of contact, "^he metal formed was 

 equally good throughout; and there remained only a few days^ 

 labor of an engraver to unite the parts. 



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