THE 



AMERICAN JOURNAL OF SCIENCE 



.^V [THIRD SERIES.] 



-♦♦♦- 



Art. XV. — The Magnetic Field in the Jefferson Physical 

 Laboratory ; by E. W. Willson, Ph.D. 



The Jefferson Physical Laboratory of Harvard University 

 consists of two wings each 60 ft. square, connected by a central 

 portion SO ft. in length. The western wing is allotted exclu- 

 sively to original work and special research, and is constructed 

 wholly without iron. It is of course impracticable entirely to 

 exclude magnetic material from the rooms of a building devo- 

 ted to these objects, but the absence of all iron from the ma- 

 terials of the building itself, making it certain that no disturb- 

 ing cause lies hidden from view in the walls, that the gas and 

 steam pipes are of harmless material, and that a sensitive instru- 

 ment may be even set upon the floor without possible risk of 

 disturbance from the nails, is an advantage which will be appre- 

 ciated by those who are familiar with magnetic measurements. 



As the entire avoidance of iron adds largely to the cost of 

 construction of a building 60 ft. square, with three full stories 

 above a high basement, heated by steam pipes in each room 

 and well piped for gas, it is desirable to know how far the end 

 sought has been attained, and as the experiment has rarely, per- 

 haps never, been tried elsewhere upon so extensive a scale, the 

 incomplete series of observations of which I here give the 

 results have a general interest. That a complete survey of the 

 whole wing was out of the question is evident, for while these 

 observations were in progress much other work was being done, 

 some of which required the use of dynamo currents, while in 

 one of the rooms a considerable magnetic disturbance arose from 

 the presence on the floor above, of an iron stove in constant 



Am. Jour. Sci.— Third Series, Vol. XXXIX, No. 230.— Feb., 1890. 

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