416 
ON THE TOTAL SOLAE ECLIPSE OF JULY 18, 1860. 
which must have been carefully fused The collodion employed should be iodized a 
month before use with the cadmium iodizer, and, before starting, carefully decanted into 
clean vessels, tied over with bladder to prevent evaporation. 
1 would recommend that three instruments, having a focal length of about 10 feet, 
should be prepared and kept, with the portable observatory, in readiness to be placed at 
the disposal of any such expedition as that organized by the Astronomer Eoyal. These 
instruments would give pictures of the luminous prominences in four seconds at the 
outside ; and under favourable atmospheric conditions, in less than a second. 
Observers intending to take charge of an instrument should practise with it in taking 
lunar photographs, previous to starting, so as to familiarize themselves completely with 
it. Not fewer than four persons should accompany each telescope, and two of them 
ought to be accomplished photographers. 
Pictures of the partial phases would be best obtained with such an instrument as the 
Kew heliograph. 
Lastly, I have deemed it to be desirable that positive copies of the eclipse-pictures 
should be placed in some Institution readily accessible to the public, and I have there- 
fore presented to the South Kensington Museum a series of enlarged positive copies on 
glass, 9 inches in diameter, which are at present exhibited in the International Exhibi- 
tion, Class XIII. 
* “ Eeport on Celestial Photography,” by the author, in the Eeport of the British Association for 1859. 
