——_ 
ON MAGNETICAL AND METEOROLOGICAL OBSERVATIONS. 5 
“ Madras. 
“Lieut. Ludlow waited for the completion of the building of his observa- 
tory, and accordingly his regular series of observations commenced only in 
March 1841. He took the precaution of observing the time of vibration of 
all'his magnets in Dublin before starting, and on his arrival at Madras, and 
was thus enabled to select for use those whose magnetism was most steady. 
“You are aware that a perfect determination of the changes of the third 
element has been a serious desideratum in most of the observatories, the in- 
strument devised by me for the determination of the variations of the vertical 
component of the force having in most cases failed. The value of the results 
in this case depends entirely on the individual instrument, and I do not know 
any that have given good results, with the exception of those belonging to the 
observatories of Toronto, Madras and Singapore. This circumstance adds 
much value to the results of these observatories, inasmuch as the observations 
made with this apparatus cover a space of nearly three years, and of course it 
furnishes an argument for the publication of the Madras and Singapore ob- 
servations. : 
“Lieut. Ludlow cautiously avoided all the difficult. work of absolute deter- 
minations, until he found himself master of the methods; and accordingly his 
results of this kind are free from the errors which are to be found in the earlier 
observations made elsewhere. The absolute determinations commenced at 
Madras with the year 1842, 
“ Singapore. 
“The observations made at Singapore, under the direction of Lieut. 
Elliott, commenced earlier than either of the other Indian stations, namely, in 
December 1840, and (as regards term observations) in the month preceding. 
“The vertical force instrument has worked at this station perhaps better 
than at any other, and accordingly the results have a peculiar value. 
“The diurnal changes at Singapore are remarkable for their regularity, so 
much so, that the diurnal curve may be obtained satisfactorily from a very 
limited number of observations. 
“ After the example of Major Boileau, Lieut. Elliott has had observations 
taken every fifteen minutes, commencing in April 1842. I am not aware 
whether he still continues this labour. 
“ Lieut. Elliott has made, from time to time, a considerable series of obser- 
vations (simultaneous with those of the observatory) at Java, Borneo, and 
other places. 
“The atmosphere at Singapore is loaded with moisture. Lieut. Elliott has 
taken numerous observations of the actinometer ; but the place is unfavoura- 
ble and the observations unsatisfactory. 
“ Believe me to be, 
“ Dear Sir, very truly yours, 
“ H. Luoyp.” 
A letter from Professor Bache to Colonel Sabine announces the gratifying 
fact, that the Senate of the United States has ordered the publication, in 
full, at the expense of that government, of the magnetic and meteorological 
observations at Girard College, Philadelphia, and at Washington ; both which 
publications are now proceeding. 
M. Plantamour has commenced the publication of the observations at Ge- 
neva. M. Kreil has published the fifth volume of the Prague observations. 
As regards the circulation of the printed observations, arrangements have 
been made by the Royal Society for the regular communication of the Green- 
wich observations in this department to all the institutions and persons named 
