Royal Astronomical Society. 521 



" It would be well, as soon as Jupiter reaches a convenient position, 

 say during the ensuing winter and in the spring of 1850, for observers 

 generally to record their estimates of the relative brightness of the 

 satellites as often as possible. The labour of doing this will be but 

 trifling, and may lead to the discovery of the laws of these singular 

 phsenoniena. 



" We have observed Schweitzer's comet twice since its reappear- 

 ance. 



" From the circles of the great equatoreal compared with B. A. C. 

 No. 1634, we have — 



Cambridge M.T. Comet's R.A. 1849-0 Comet's Decl. 1849'0 



1849. hms hms o/// 



Aug. 24 15 37 30 4 45 0-4 -27 14 14 



26 15 38 42 4 41 5-4 -27 17 45 



" With the micrometer we have the following places : — 



Cambridge M.T. 

 1849. hms m s / // 



Aug. 24 15 37 30 Comet follows * in 34-75 Comet N. of * by 7 36-5 

 26 15 38 42 precedes * by 3 20-35 N. of * by 4 5-7 



* is Lacaille 1613, whose place seems to be erroneous in N. P.D. 



"The star Lalande 9167, of the 7'8 magnitude, is missing." 



The Astronomer Royal exhibited an instrument for performing 

 arithmetical multiplications and divisions, constructed under the di- 

 rection of William Bell, Esq., Coronation Road, Bristol. The Pre- 

 sident remarked, that for mere exhibition of the significant figures 

 produced by a single multiplication or division, to a certain degree 

 of accuracy, nothing could be more convenient than the common 

 sliding rule containing two similar scales, one fixed and the other 

 moveable, in which the lengths corresponding to the numbers re- 

 presented are the logarithms of those numbers corresponding to a 

 certain modulus. In the scales of this kind in common use at the 

 Royal Observatory, the distance from 1 to 10 upon the scale is about 

 12 inches; and with these dimensions, a product or quotient will be 

 accurate, with the roughest degree of attention, to -g^ part ; an ac- 

 curacy which sufiices for a vast amount of the small calculations in 

 an observatory. And with proper scales for trigonometrical functions, 

 the problems of plane and spherical trigonometry can in most cases 

 be easily solved. These inconveniences, however, attend it : — 1st. It 

 cannot be conveniently applied to multiply three or more quantities, 

 or in general to exhibit a product of even two which is given in a 

 different denomination ; as when a sine is given by the product of 

 two tangents ; this failure, however, may usually be remedied by the 

 use of two parallel sliders. 2nd. When used to multiply numbers, 

 it gives no information as to the place of the decimal point in the 

 product. It is to remove some of these inconveniences, but espe- 

 cially the last, that Mr. Bell has constructed his instrument. 



The logarithmic spaces in Mr. Bell's machine are arranged upon 

 a circle, a single series of numbers from 1 to 10 occupying the entire 

 circumference. This construction, as is well known, may be used 

 in the same way as the common sliding rule ; but, like it, it gives no 



