320 Application of Photography to the Self-registration 
cation to the Royal Society in 1847,* and the advice and instruc- 
tions with which the writer has been favored by him from 
time to time, in the establishment of one at Toronto. The vari- 
ous changes in detail which have been suggested by experience 
since the date of the paper referred to, and the possibility that 
the present communication may promote the establishment of 
other registers on this continent, will afford, it is hoped, a sufficient 
apology for its want of originality. 
“In order to render any method of photographic registration 
practically useful, it is essential that the three following indica- 
tions should be fu 
“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 a 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 union of the three conditions is represented by a suspended 
of the fluid, and is calculated, with perfectly good camphine, to 
burn twelve hours without requiring attention—in general it will 
be necessary to attend to it every six hours, by cutting off the 
charred end of the wick and refilling. A circular opening about 
1-2 inch in diameter is made at the top near the centre of the 
side which is presented in front, this is stopped with a bone or 
ag ai aed 
* “Description of an a tus for the Automatic Registration of Magnetometers 
and other Metoortiagiaat tents by Photoiraphy.” By Charles Brooke, MB., 
F.R.S., &. Philos, Trans. 1847. 
