THE SMITHSONIAN INSTITUTION. 17 



Observations continued for a certain time at different periods along 

 the coast of the Pacific, and compared with the photographic ret^ords 

 obtained by the apparatus in tli^is Institution, would afford interesting 

 results as to the simultaneous perturbations of the magnetic force at 

 distant places on the same continent. 



Under the head of magnetism, it may be mentioned that a complete 

 set of apparatus has been obtained from Ruhmkorff", of Paris, for ex- 

 hibiting the facts of the new branch of science called dia-magnetism. 

 A few years ago, but four metals were known to possess magnetic 

 properties, namely, iron, nickel, cobalt, and manganese. It is now 

 known that all bodies exhibit analogous phenomena when placed under 

 the inductive influence of powerful magnets ; but they are not all simi- 

 larly affected. All bodies may, however, be divided into two classes : 

 one in which polarity is developed at the extremities of a bar of the 

 vSubstance, as in the case of iron, and hence called simple magnetic 

 bodies ; and the other class, in which the polarity is transverse to 

 the length of the bar, and the substance is hence called dia- magnetic. 

 The simple repetition of these experiments in this country is of im- 

 portance, and the apparatus may serve as a model for imitation to our 

 ingenious artists. 



'(3.) On the 26th of last May, the central track of an annular eclipse 

 passed over the northern part of the United States. Tiie eclipse itself 

 was visible over almost the entire area of the North American conti- 

 nent ; and as no obscuration of the sun of equal magnitude would 

 again occur in this country until 1865, it was important that all the 

 facilities possible should be afforded for observing its different epochs 

 and pliases, as well as the concurring phenomena. For this purpose, 

 in conjunction with the superintendent of the Nautical Almanac, a large 

 map, exhibiting the times of beginning and ending, and the amount of 

 obscuration and phases of the eclipse for every part of the United 

 States, Canada, and Mexico, together with tables and explanations, 

 were prepared and distributed to all thp observers in correspondence 

 with the Smithsonian Institution. A set of minute instructions, pub- 

 lished under the direction of the American Association tor the Advance- 

 ment of Science, was also presented to the same persons. Unfortu- 

 nately, the weather proved cloudy over a considerable portion of the 

 space covered by the central part of the shadow, though a number of 

 interesting observations were made. The expense of the map and 

 tables were defrayed jointly by this Institution and by the appropria- 

 tion for the Nautical Almanac. 



The results of the observations, so far as they have been reported, 

 have been published in the Astronomical Journal, edited by Dr. B. A. 

 Gould, jr., Cambridge, Massachusetts. They are illustrated by pho- 

 tographic impressions of the sun, made under the direction of Profess(jr 

 Bartlett, at West Point, and also by others, made under the direction 

 of Professor S. Alexander, of Princeton, New Jersey. The expense of 

 these was borne by the Institution, for which full credit has been given. 



1 may mention in this connexion that Professor Cofhn, of Lafayette 



College, Pennsylvania, has presented to the Smithsonian Collections an 



interesting map, on which are delineated the paths or central tracks of 



all the great solar eclipses of the nineteenth century which traverse the 



Mis. Doc. 24 2 



