74 J. Waterliouse — Photography in connection with [No. 2, 



After further practice, a second full rehearsal took place on the 2nd Decem- 

 ber, and a final one on the 6th, which was very successful ; 120 six-inch 

 plates with 6 Janssens being exposed in the course of the time the Transit 

 was calculated to last. 



The preparations for the Transit itself, such as numbering and cleaning 

 glasses, preparing and testing baths, and examining the minor adjustments 

 of the instruments were commenced about a week beforehand. 



Unfortunately the weather for a few days before the Transit was very 

 cloudy and most unfavorable for trials of chemicals and testing the focal 

 adjustments of the instrument, which caused some trouble and uncertainty. 



Although it was determined to adopt the wet process entirely 

 for the Transit plates it was considered desirable to have a small 

 supply of dry plates prepared in reserve in case of accidents and to 

 be used, if necessary, at times when the supply of wet plates could 

 not readily be kept up. About a dozen of the six-inch and four of the 

 Janssen plates were therefore prepared by the coffee-albumen process, already 

 described, using a highly bromized collodion recommended by Captain Abney 

 for sun pictures, which gave an intense picture with considerable sensitive- 

 ness ; but owing to the short time between receiving the materials from 

 England and their being used this collodion had scarcely time to ripen 

 properly, and so could not have a fair trial. Captain Abney's formula was — 



Thomas' bromized collodion 20 oz. 



„ iodized „ 20 „ 



Alcohol s. g., 805 6 to 8 „ 



Pyroxyline 300 grs. 



Water - 120 min. 



The plates were developed with the strong alkaline developer recom- 

 mended by Captain Abney. 



One of these Janssen plates and four of the six-inch plates were used 

 during the Transit and, with the exception of the spots, were excellent pic- 

 tures, fairly sharp and dense, free from blurring, and, in some respects, better 

 than many of the wet plates. 



Several days before the Transit 120 six-inch glasses were selected from 

 those set aside as the best and were numbered with a diamond in one corner 

 consecutively from 1 to 120. A reserve of about 30 plates was also selected 

 and marked with a cross in one corner. The whole of these plates as 

 well as a dozen of the best circular Janssen plates were then carefully 

 cleaned and coated, on the unmarked side, with an albumen substra- 

 tum, consisting of the white of one egg and about one drachm of 

 ammonia to a wine-bottle of water, in order to prevent any rising 

 of the film and consequent liability to shrinkage. The plates thus 

 numbered and albumenised were arranged in order in five boxes, hold- 



