REPORT OF THE SECRETARY. 37 



dieting, with unerring certainty, the approach of storms. But in the 

 course of a number of years the average character of the climate of 

 the different parts of the country may be ascertained, and the data 

 furnished for reducing to certainty, on the principle of insurance, what 

 plants can be most profitably cultivated in a particular place ; and it 

 is highly probable that the laws of storms may be so far determined 

 that we shall be able, when informed by the telegraph that one has 

 commenced in any part of the country, to say how it will spread, and 

 whether it may be expected to extend to our own locality. We make 

 these remarks in order to prevent disappointment and the evils pro- 

 duced by exciting expectations which cannot possibly be realized. 



Terrestrial Magnetism. — Nearly a continuous record of the changes 

 of magnetic declination has been kept up by the photographic method, 

 during the greater part of the past year, at the magnetic observatory 

 established by the Institution and the United States Coast Survey. 

 The series was interrupted, in December, by some improvements in 

 the arrangement of the building, and by preparations for the mount- 

 ing of additiorfkl instruments for recording the changes of horizontal 

 and vertical force. The apparatus was constructed, at the request of 

 Professor Bache, under the direction of Charles Brooke, Esq., of Lon- 

 don, who originally designed this method of registration, and who 

 kindly undertook to adjust all the delicate compensations. Similar 

 instruments are in operation at the magnetic observatories of Green- 

 wich, Paris and Toronto ; and it is hoped that a continuous correspond- 

 ing record will in future be made here, which will prove of great 

 interest and utility in the study of the phenomena of terrestrial mag- 

 netism. 



The set of portable magnetic instruments for absolute determina- 

 tions belonging to the Institution are placed in charge of Baron 

 Muller, who is making a scientific expedition to Mexico and Central 

 America. Recent investigations having shown that magnetic obser- 

 vations in those regions, where none have been made since Humboldt 

 visited them, more than fifty years ago^ would have a special value in 

 determining the law of distribution, the Institution availed itself of 

 the opportunity offered by Baron Muller' s expedition, to forward this 

 branch of knowledge by furnishing instruments, and appropriating an 

 amount adequate to cover the additional expenses occasioned by these 

 observations. Full copies of the records are transmitted to the Insti- 

 tution as opportunity offers. The results of the observations, as far as 



