1875.] the Observation of 'the Transit of 'Venus. 77 



ing the change, and this he was ordered to do at all changes from wet to 

 dry and vice versa. 



In order to prevent mistakes and confusion in communicating between 

 the dome and the dark room, it was arranged that all communications should 

 be in writing ; supplies of slips of paper with a pencil attached were kept 

 in a convenient position in different parts of the dark room and the dome, 

 and were passed to and fro through the slides in the doors without noise or 

 disturbance of the operations. 



Of the three native servants, one remained in the dark room to hand 

 the dark slides backwards and forwards, but when the Janssen slide was 

 used he went into the dome to put on the No. 2 counterpoise, at the object 

 glass end of the telescope ; another man remained in the space between the 

 double doors and passed the dark slides in and out through the slides in the 

 doors. The third stood in the dome to hand me the dark slides, hold the 

 loops of thread and hook them on the string attached to the exposing shutter, 

 turn the dome, and give me any other assistance I required. 



Corporal George and Private Eox took it in turns to act as orderly of 

 the week and their duties were to open the dome for work, have the water 

 boxes filled at the proper times, uncover the instrument, see that the 

 necessary chemicals and glasses were ready in their places for use, and after 

 work, to have the rooms cleaned, the instrument dusted, and the dome 

 closed. 



Two or three days before the Transit I examined all the adjustments of 

 the sliding shutters and the electrical communications and satisfied myself 

 that all were in good order. 



As the weather had been cloudy two or three days before the Transit 

 there was some uncertainty as to whether it would be fine or not, but, in the 

 event of its turning out cloudy, I had arranged that the whole operations 

 were to be gone through just as for a drill, so that we should have been in a 

 position to take immediate advantage of any break in the clouds, discretion 

 being of course exercised in altering the uniformity of the intervals between 

 the plates, in order to take advantage of any passing gleam of clear sunshine. 

 Fortunately it was fine and this precaution was not required, but I am sure 

 that it was the only way of making certain of being ready at a moment's 

 notice had the sky been cloudy. 



Operations on the Day of the Transit. — After the cloudy weather 

 of the previous two days, it was an agreeable surprise when we awoke on 

 the morning of the Transit to find an almost cloudless sky. All prepara- 

 tions had been completed the night before and we were in our places 

 betimes. As the first contact had been computed to occur at about 7h. 

 13m. 7s. (mean time) the order for commencing the preparation of the 

 plates was given about 7 o'clock, and the work of the day commenced 

 with the exposure of a Janssen plate for trial of the apparatus. After 



