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1873.] President's Address. 59 



The last transit of Venus took place in 1760, more than a century 

 since ; and it needs but little consideration of the immense improvements 

 which have been made in the accuracy of construction of astronomical instru- 

 ments, in the preparation of telescopes, and above all in the marvellously 

 beautiful application of photography in self-recording instruments for such 

 transient phenomena, to see that there is not only a well founded hope, 

 but a certainty, that the determination of the elements of the vast calcula- 

 tions to be based on the phenomena will be far more careful and more accu- 

 rate than before. Fortunately also, another transit will recur within a short 

 interval or in 1882, and with the experience gained in 187-1 and the extension 

 of points of observation contemplated for 1882, we may I think confidently 

 look forward to seeing that all-important determination of the distance of 

 the earth from the sun established with extreme accuracy. On this, as is 

 well known, depend all the dimensions of the solar system. The British 

 Government have undertaken the provision of instruments and observers for 

 five stations. These are selected with a special view to their value, as en- 

 abling the best observations to be carried on. These five stations are, Oahu 

 in the Sandwich Isles, Kerguelen Island in the Indian Ocean, Eodriguez a 

 dependency of Mauritius, Auckland in New Zealand and Alexandria. Of 

 the three first in the list, the longitude is to be determined accurately by a 

 whole year's series of observations. Further, owing to the distance, the 

 parties of observers must leave England more than six months before the time 

 of transit. Instruments alone will cost considerably more than £10,000, 

 conveyance, pay, sustenance as much more. This may seem a large sum, 

 but as compared with the object in view, it is as nothing. The acquisition of 

 knowledge of so much importance to all civilized nations, and the seizing 

 on an opportunity of rare occurrence for fixing some of the most important 

 astronomical and cosmical questions alone would have justified, nay would 

 have demanded, the outlay of almost any sum. And I have no reason to 

 doubt, that the answer to the suggestion to carry out this most important 

 observation in a fitting manner from the head of the Treasury in Great 

 Britain would have been precisely the same, ' they have no objection to offer 

 to the expenditure, were the sum required ten times what it is.' 



In addition to the stations thus specially selected, the observatories of 

 Melbourne, and Sydney, of the Cape of Good Hope, Madras and Bombay, will 

 all be utilized. The whole sea board of the United States of America, and 

 he Canadian localities will all be favourably situated for certain obser- 

 vations and we may safely trust that the well known energy and zeal of our 

 American brethren will not fail them here. To supplement the observations 

 in the southern Hemisphere, by others in the northern, we must look to the 

 Bussians who have in their widely spread territories many localities admir- 

 ably adapted for such observations. For one special class of observations 



