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VII. On the Automatic Registration of Magnetometers , and other Meteorological 
Instruments , by Photography. By Charles Brooke, M.B., F.R.C.S.E. Com- 
municated by G. B. Airy, Esq., F.R.S., Astronomer Royal. 
Received June 16, — Read June 18, 1846. 
An efficient method of continuously registering the variations of magnetometers 
having been generally admitted to be a desideratum in science at the Magnetic 
Conference held during the Meeting of the British Association at Cambridge, it 
became a matter of philosophical interest to supply the deficiency, and this, it is 
hoped, has by the following means been satisfactorily accomplished. 
As the mechanical force which a suspended bar magnet is capable of exerting, 
during its variations of direction, is far too minute to actuate the most delicate 
mechanism without sensibly affecting its position, the desired object will probably 
be obtained by photography alone. In order to render any method of photographic 
registration practically useful, it is essential that the three following indications 
should be fulfilled. 
First, to obtain an easily managed artificial light of sufficient intensity to affect 
photographic paper, especially at those periods when it is of most consequence to 
obtain a continuous register, namely, when the position of the magnet is undergoing 
great and rapid variations. 
Secondly, to prepare by a ready process photographic paper sufficiently sensitive 
to receive the feeble impressions of artificial light, and at the same time sufficiently 
durable to retain those impressions during a period of at least twelve hours, as a 
more frequent attention to the apparatus would probably interfere with the ordinary 
arrangements of an observatory. 
Thirdly, to magnify the movements of the magnet by some optical arrangement, 
so that the variations may be indicated with sufficient minuteness and accuracy. 
The first point may be attained by a camphine lamp, the light of which is much 
whiter and more intense than that of any other known lamp ; that which has been 
in use (see fig. 3, Plate V.) is of a square form, each side being 2^ inches long and 
high, and stands in a little wooden frame made exactly to fit it, that it may with 
certainty be replaced in exactly the same position, if removed for the purpose of 
being trimmed. Many registers prove this to have been the case, there not having 
been any visible displacement of the line at the recorded period of removal of the 
lamp. The wick is flat, and about 0*5 inch wide, and inserted near one corner of 
the lamp, that the reflected pencil may not be obstructed in its passage ; and a feeder 
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