3S0 Notices rexpccting New Books. 



^sec.\i fiom Greenwich, as determined bj- a triangulation connecting 

 it with the Royal Observatory at the Cape. The altitude was found, 

 by barometric measurement, to be about 142 feet above the mean 

 sea level at Table Bay. 



For the purpose of working the sweeping and other mechanical 

 movements of the reflector and executing necessary repairs, Sir John 

 engaged the services of an attendant, who, besides possessing the 

 qualifications of a ready mechanic, had acquired considerable expe- 

 rience in the management of the instrument during the review of the 

 northern heavens. With the exception of this indispensable aid, 

 " the whole of the observations, as well as the entire work of re- 

 ducing, arranging, and preparing them for the press," were executed 

 by the author himself, ^^'e risk little in asserting that the annals 

 of astronomy afford no more remarkable example of the patience of 

 the observer and computer united with the highest order of genius 

 than that which is furnished )jy the present volume. 



Sir John left the Cape about the end of January 183S, having 

 passed four years and a few days in the colony. Making every 

 allowance for the energ)-, skill and experience of the observer, so 

 great a multitude of difficult observations (not merely for ascertain- 

 ing the places of the various ol)jects which came under review, but 

 their peculiarities of aspect and physical structure for which atten- 

 tive and repeated examination was frequently necessary) could not 

 possibly have been accumulated in so short a period of time except- 

 ing under tolerably favourable conditions. The climate of the Cape, 

 he observes, must be regarded as on the whole favourable for astro- 

 nomical observations, though tliere are some drawbacks. In the hot 

 season, from October to March, the nights are for the most part su- 

 perb ; but in the vicinity of the mountains the south wind frequently 

 brings with it a belt of clouds, extending many miles from the hills, 

 and cutting off the view of the sky. \^ery often too, the excessive 

 heat and dryness of the plains gives rise to a disturbance of the opti- 

 cal tranquillity of the air, and greatly impairs distinct vision ; the 

 images of the stars being in some cases violently dilated, and con- 

 verted into ill-defined nebulous balls or puffs of 10' or 15'' in dia- 

 meter ; in others forming round pellets of 3" or 4" in diameter, unlike 

 spurious discs, and rather resembling planetary nebulre ; while on a 

 few occasions the appearances have been very perplexing, and such 

 as there is difficulty in accounting for on any optical principle what- 

 ever. In the cooler months, from ]\Iay to October inclusive, and 

 particularly in June and July, the finest opportunities occur ; the 

 state of the atmosphere is in these months habitually good, and im- 

 perfect vision is rather the exception than the rule. The best nights 

 occur after the heavy rains, which fall at this season, have ceased for 

 a day or two. On these occasions hardly any limit is set to magni- 

 fying power except what the aberrations of the specula necessitate. 

 Among the phaenomena incidental to the climate he makes mention 

 of a " nebulous haze," which comes and disappears very suddenly, 

 and of which the effect is to convert every star of the 9th magnitude 

 and upwards into a " ne1)ulous star," i. e. a well-defined star sur- 



