198 Scientific Intelligence. 
7. Magnetic Variations.—Prof. B. Silliman, Sir—I observe in 
the April number of the American Journal of Science and Arts, the 
result of a series of observations, and calculations to ascertain the 
variation of the compass needle. In the year of 1827 in Troy, 
N. Y. I made some observations myself for the same purpose ; I will 
send you my result, and if you think it worth an insertion in one of 
the numbers of your Journal, it is at your service. 
~ 1827, June 24th.—The result of twelve observations of the sun, 
in both forenoon and afternoon, of Altitude and Azimuth, in mean. 
In forenoon Alt. 22° 21-—Az. N. 83° 51’ E. 
In afternoon Alt. 22° 21’—Az. N. 71° 42’ W. 
2 | 12° 09 
Magnetical variations —- - N. 6° 04.5’ W. 
Yours most respectfully, 
Aupert DankeERr, 
Civil Engineer and Land Surveyor, and Member of Rensselaer School. 
Troy, N.Y. August 18th, 1829, 
8. Elements of Technology, by Jacob Bigelow, M. D. late Rum- 
ford Professor in Harvard University, 8vo. pp. 507, Boston.—This 
book is taken chiefly from the lectures delivered by Professor Bigelow 
at Cambridge, and is intended for students, to whom it must be an 
acceptable present. It presupposes, in the reader, a knowledge of 
scientific principles ; but takes him, thus prepared, by the hand, and 
jeading him round, shews him the application of these principles to 
a variety of the most useful and familiar arts. The information it 
contains, while most desirable, is such as is frequently not to be found, 
except in scarce and voluminous authors; some of it, that on arch- 
itecture for instance, we have frequently known to be sought after in a 
manner to make us regret that it was not more accessible. If we were 
inclined to qualify our favorable opinion of this work, we should per- 
haps say, that the multiplicity of articles, and the consequent brevity 
of each, may have hindered the author from being as copious and 
thorough-going on all of them as he would no doubt, have wished to be 3 
but the book is intended to be practical ; and practical scientific men, 
while they lead the community, must not go too far ahead. The 
author himself, is certainly at home in science ; his book shews @ 
| familiar acquaintance with his subject ; the matter is well selected and 
the style lucid and happy. The reader will find himself at the end 
