316 Annual Report on the U. S. Coast Survey. 
have been accustomed to see graduations, but to single seconds 
of arc, each of these seconds occupying one-tenth of an inch. 
The latitudes have been determined from numerous observations 
with the zenith section, and the difference of longitude of two 
exterior points, by the transportation of chronometers. 
We are here presented with a test of quality which may be 
applied to the maps of our coast survey. Ist. The scale adopted 
by Mr. Hassler for the details of the maps was ;;4,,, or a little 
less than six inches to the mile. As the object of the work is to 
combine a chart for navigation with a map of the coast, this is 
too large for practical use except in the case of isolated harbors, 
8 CO 
the American sheets, greatly surpass those of the celebrated map 
just mentioned. 2d. The system of topographical details intro- 
duced by Dr. Bache, secures uniformity in the representation of 
the ground and includes all that is alluded to in the foregoing 
account. The horizontal curves drawn at regular vertical dis- 
tances, are marked in red, and the system of hachures adopted, 
is modified from that of Lehman. 3d. The scale admits of the 
same subdivision as those of the British maps; the numerous de- 
terminations of latitude resulting from the discovery before re- 
ferred to in regard to discrepancies of the geodetic and observed 
latitudes of near stations, are reduced to central points by the 
geodetic results; the determinations of difference of longitude 
made by the electro-magnetic telegraph, give materials of the 
same kind and quality as those alluded to in praise of the trans- 
atlantic maps. In the case of the longitudes, the operation of 
which is still in progress, a method is employed a step in advance 
of those abroad. 
The large plates of copper on which the charts are delineated, 
are produced in a finished state ready for the engraver by means 
of an electrotype process. Also, the same principle is applied 
to multiply the plates after they are engraved, so as to increase 1n- 
definitely the number of impressions which may be obtained 
while the original plate remains uninjured. 
Leplorations of the Gulf Stream.—In the last report an ac- 
count was given of a series of observations on the Gulf Stream, 
made by Lieut. Geo. M. Bache, whose life fell a sacrifice to his 
zeal in the discharge of his duty, and whose loss science was 
called upon to mourn just as he was commencing with his ac 
eustomed ardor, the investigation of one of the most interesting 
phenomena of our globe. The results he obtained will be give" 
to the world in another publication, and it will be sufficient for us 
to state in this place that he examined three entire sections across 
the stream. His researches exhibit the remarkable fact, that the 
whole current of warm water to the depth of at least four b 
i acallaies Blais 
