ON THE MAGNETIC INTENSITY OF THE EARTH. 25 
de Janeiro. He made also a very extensive series of intensity 
observations on board ship in his passage from Kamtschatka 
to Europe. Of these he has not yet communicated the nume- 
rical results. He observed the vibrations of a dipping-needle 
placed on an apparatus contrived to guard against the ship’s 
motion, which is understood to have been very successful*. 
Kupffer, 1829.—These observations were made in a scien- 
tific journey to the Caucasus, undertaken by the order of the 
Emperor of Russia. M. Kupffer was furnished with two 
- horizontal needles, one of which he received from M. Hans- 
teen, and the other from myself through M. de Humboldt. 
He employed them, between May and August, 1829, at St. 
Petersburg, Moscow, Stavropol, two stations in the Caucasus, 
Taganrog, and Nicolaieff; and on his return to St. Petersburg, 
presented to the Imperial Academy of Sciences a report on 
the general results of his journey, in which the times of 
vibration of the needles are specified, together with the tem- 
peratures and the observed dips; but the conclusions, in 
regard to the relative intensity at the different stations, were 
deferred, until the corrections for temperature for the two 
needles could be experimentally investigated. I am indebted 
_to M. Kupffer for a printed copy of this report, and I have 
* Since this report passed from my hands into those of the Assistant-general 
Secretary, I have been favoured by M. Erman with a complete copy of his ob- 
servations, including those made at sea. On hearing from M. de Humboldt 
that I was engaged in drawing up this report, M. Erman, with great liberality 
and most obligingly, sent me a copy in manuscript of the whole of his results 
provisionally computed. I have thus been enabled to add five or six stations 
between Ochozk and the harbour of St. Peter and St. Paul with which I was 
previously unacquainted, and 167 observations made on his voyage from Kamt- 
schatka to Europe. I consider these last observations particularly valuable, in 
the evidence they afford, that determinations of the intensity can be made at 
sea with an accuracy but little inferior to those on land. With the exception 
of a few in the very early part of the voyage, which appear from some cause to 
give somewhat lower intensities than accord with M. Erman’s own observations 
at Sitka and St. Francisco, the results, both in the Pacific and Atlantic, when- 
ever they approach the land stations of other observers, present a most satisfac- 
tory accordance. 
The complete series of M. Erman’s magnetic determinations is the most ex- 
tensive contribution yet made to the experimental department of magnetical 
science ; nor can we rate its value too highly, since it furnishes us with conse- 
_ cutive determinations of dip, variation, and intensity, by the same highly qua- 
lified observer, and with the same excellent instruments, extending through all 
the meridians of the globe, and from the Arctic circle in Siberia to nearly 60° of 
south latitude, the whole of this distance being traversed in the course of two 
_ years, and the track completely marked by the frequency of the observations. 
