LOCAL PARTICULARS OF THE TRANSIT OF VE^rS, 1874. 77 



probably on the dry plains about Urana, where there seems to be 

 a singularly clear atmosphere. 



Of other stations to be occupied in Australia I at present only 

 know of Melbourne, Adelaide, and Brisbane. But it is probable 

 that Victoria will have two other stations, though this is not yet 

 decided. I have no doubt also that Mr. Tebbutt will observe at 

 Windsor ; so that the best part of Australia will have such a 

 mmiber of stations as will give us a fair chance of blue sky some- 

 where. Now, if a line be supposed to be drawn through Sydney, 

 Mundooran and Palmerston in Northern Australia, all jDlaces on 

 that line will see first contact at the same time as Sydney, viz., 

 12h. 4m. p.m. December 9th. All poiuts to the east of this line will 

 see it earlier, and all points to the west of it will see it later. If 

 a line be drawn through Brisbane, parallel to the line described, 

 it will indicate all places at which first contact will be one minute 

 earlier than Sydney. A similar line through Melbourne will 

 indicate places one minute later than Sydney. 



The point on the sun's disc where Venus will first be seen is 

 situated 49 degrees from the north point of the sun towards the 

 east, or on the lower right hand side as we look at the sun, half- 

 way between the lowest (north) point of the sun, and the east 

 side. If an inverting (astronomical) telescope is used, it will be 

 49 degrees from the upper limb towards the west or following side. 



We now come to the particulars of observations ; and first as 

 to the instruments. I will describe as briefly as possible some of 

 the principal forms. The great majority of the telescopes which 

 are to be used have an aperture of from 4 to 5 inches (or stopped 

 down to that), and it is decided that a magnifying power of 150 

 will be best for general purposes. The telescopes to be used for 

 photographic work are for the most part of the same size, but the 

 longer the focal length and the larger the object-glass for this 

 purpose, the better. They all, with the exception of the American 

 form, to be described presently, will be provided with a combina- 

 tion of lenses inserted in the position of the ordinary eye-piece, 

 which vnl\ enlarge the picture of the sun to about 4 inches. The 

 enlarging combination may be either an ordinary low power 

 Huygenian eye-piece, a short-focus camera combination, or one 

 made by fixing the object glasses of a binocular with their convex 

 sides together, as indicated at L (figure 8) . The latter form I 

 have found very satisfactory. A camera box will also be attached 

 firmly to each of the telescopes holding the plate at P, (figure 8). 

 At S, where the rays cross, the flashing shutter is to be inserted. 



The American form of photo-telescope is totally difl^erent. It 

 consists of an object-glass of about 5 inches diameter and 40 feet 

 focus, corrected only for photographic or actinic rays. It is to 

 be mounted with its tube horizonal and true north and south, but 

 the object-glass and camera are to be supported on brick or 



