82 J. Waterhouse — Photography in connection with, Sfc. [No. 2, 



by the use of moist plates, prepared with bromised or bromoiodised 

 collodion afterwards treated with albumen and glycerine, which I have found 

 very simple to prepare and exceedingly free from all tendency to blurring 

 or irradiation. It is probable, however, that before 1882 the usual modes 

 now in vogue for taking negatives will have been quite superseded by the 

 simpler method of using sensitive emulsions which have only to be poured 

 on to the plates and dried without any further preparation. Great advances 

 have recently been made by Carey Lea, Bolton and others in obtaining such 

 emulsions capable of giving pictures with the same rapidity as the ordinary 

 wet or dry processes and with a perfect freedom from the irradiation or blur- 

 ring so detrimental in astronomical photography, besides which the perfect 

 simplicity and ease of the operations are a strong recommendation ; and I 

 may, I think, safely predict that should photography be used for the next 

 Transit, the emulsion processes will, if not exclusively, be used very extensive- 

 ly ; unless, possibly, the superiority of pictures taken on daguerreotype plates 

 or silvered glass films over those on collodion should be incontestably proved 

 or some other better process be discovered meanwhile. 



Although the photographic operations connected with the obser- 

 vation of a Transit of Venus present no great difficulties, and are in 

 some respects easier than photographing the total phase of an Eclipse, a 

 great deal of patient careful work is required beforehand to ascertain 

 the best conditions for working with regard to local circumstances, and 

 this the short time at my disposal on the present occasion scarcely 

 allowed me to have, especially as so much time was spent over the 

 dry process, which might, as the event proved, have been well employed in 

 perfecting the wet. It is therefore very desirable that the subject should 

 not be lost sight of between this and the next Transit and that every oppor- 

 tunity should be taken of utilising the experience already gained towards 

 ascertaining the most perfect methods of taking these sun-pictures. It would 

 also be advisable that as many as possible of the observers of the last 

 Transit should also take part in the next. 



Although the Transit of 1882 will not be visible in any part of India, 

 much useful preparatory photographic work might be done concurrently 

 with the daily observations of sunspots, now that an instrument is available 

 for taking advantage of the comparatively fine weather enjoyed in this 

 country, particularly at the time of year when the weather in Europe is 

 most unfavourable to such observations ; and this would not be the least 

 among the many advantages to Science to be gained by the establishment of 

 a Solar Observatory in this country, which has been so earnestly advocated by 

 Col. Tennant and, it is to be hoped, will soon be an accomplished fact. 



