1 B M .] Imperial Institute. 153 



The difference between summer and winter is 1 *34". This can 

 only arise from the refractions which are greater and less certain in 

 winter than in summer. The obliquity drawn from the summer 

 solstice surpasses that of the tahles by half that difference. We 

 see that the (able of refractions of the board of longitude, makes 

 the solstices agree much better with each other than the other 

 tables; since astronomers of reputation have found as great a dif- 

 ference as 8 or 10" between the summer and winter solstice. M. 

 Delambre in the 12 solstices which he observed, never found a 

 greater difference than ■{", even wih Bradley's tables. The table 

 of refractions which he made, in order to make the two solstices 

 Bffree with each other, and which had obliged him to reduce the 

 height of the pole to 13 for the imperial Observatory, does not 

 differ from that of the Board of Longitude from the zenith to 80°, 

 but by quantities scarcely appretiable, and which depend chiefly 

 upon the thermometrical factor. 



The new solstices are four in number. If we suppose that the 

 advantage of the circle of Reichenbach over that of Borda, is as 

 :] lo 1, it will be proper to take the mean between the two deter- 

 minations, which will reduce almost to nothing the difference 

 between the tables and direct observation. But be that as it may, 

 we sec that the height of the pole, the obliquity, and even the 

 fraction^, are as well known as can be expected; and that there 

 remain only differences so slight, that we may at pleasure ascribe, 

 them either to observation or theory, or divide them equally between 

 both. 



These observations of the sun offer likewise a very satisfactory 

 agreement, though not quite so great as that of the stars. In 181 1, 

 though the weather was very unfavourable, the difference between 

 the two extremes only once amounts to 3S". In June 1S12, it 

 only once amounts to 2 // ; in December, 1812, the weather was 

 so bad, that the difference amounted to 4*6"; and in June, 1S13, 

 it was 'l-'t" ■ 



Account of a planetary Clock, contrived by M. Gerardot. 



tount qj tne Revolutions of the heqvenly Bodies, imitated by 

 the Xfet h mism of Whirls. By M. Janvier. 



The first of these machines will excite astonishment, if we con- 

 r that the contriver of it had no knowledge of mechanics and 

 astronomy, but what he acquired himself, without any other assi t- 

 ance than a book of the most elementary kind. The machines of 

 M. Janvier are the most perfect that can be produced by a man of 

 science and a consummate artist. 



Tt trical Operations executed in Holland. By M. the 



ral Krayenhoff*. 



A great geographical undertaking, executed with all the care 

 and , i employed in the measurement of degrees. 



Spherical Trigonometry . By M. Puissant. 

 This i~ an extract of a work which will soon appear, and which 



5 



