REPORT OF THE SECRETARY. 43 



a tidal station. Key West is situated in latitude 24° 33' north, lon- 

 gitude 81° 41' west, and is a low coral island, rising at no point more 

 than ten or twelve feet above the sea. The mean temperature of the 

 spring is 75°, of summer 82°, of autumn 78°, and winter 69°. The 

 daily variation of temperature is therefore very small, and on this 

 account as well as from its position, the island is well adapted to mag- 

 netic observations, 



The observatory is situated on the grounds of the government, a few 

 hundred yards from Fort Taylor, and near the water. A large shed 

 belonging to the fort was made use of, by permission of the engineer 

 department, as an outer protection for an inner building containing 

 the instruments. The inner rooms were properly inclosed in a sub- 

 stantial manner, leaving a clear space between their walls and those 

 of the outer building for the free circulation of air. The piers sup- 

 porting the instruments rest upon the solid rock of the island, and are 

 therefore subject to no other changes than those which result from the 

 slight annual variation of temperature. A small building to the north 

 of the observatory was erected for the instruments employed to determ- 

 ine the absolute values of the magnetic elements, to be used in con- 

 nection with the continuous photographic records of the variations. 



The instruments were mounted at Key West in January and Febru- 

 ary, 1860, by Prof. W. P. Trowbridge, assistant in the United States 

 Coast Survey, and a series of observations commenced by this gentle- 

 man, assisted by Mr. Samuel Walker, in March, have been continued to 

 the present time, under the charge of Mr. George D. Allen, who is now 

 retained as permanent observer. The expense of the observations is 

 sustained jointly by the Smithsonian Institution and the Coast Survey. 

 In the appendix to the last report will be found a minute description 

 of the self-recording instruments here referred to, and of the method 

 of using them, prepared by Mr. J. E. Hilgard; and in the appendix 

 to the present report it is proposed to insert a communication from 

 Gen. Sabine to the Royal Society of London, giving a brief exposition 

 of the laws of the phenomena of the larger magnetic disturbances, as 

 far as they have been ascertained, and of the interesting contributions 

 to science which such observations as are now made at Key West may 

 be the means of affording. 



Laboratory. — During the last year the laboratory has remained 

 under the direction of Dr. B. F. Craig, of this city, and, as in former 

 years, many minerals from different parts of the country, submitted 

 to the Institution for examination, have been reported upon. It 



