364 Mr. F. Baily on Mr. Babbage's new Machine for calculating 



alluding to the tables of the other planets, which are all liable 

 to similar observations : but I shall take the liberty of calling 

 their attention to those very useful tables which have from 

 time to time appeared for determining the apparent places 

 of the fixed stars; and which generally assume the title oi 

 " Tables of Aberration and Nutation." Tables of this kind 

 are of vast importance to the practical astronomer, since they 

 save a great deal of time and labour in the reduction of obser- 

 vations : and it. is believed that many valuable observations re- 

 main unreduced, for want of convenient tables of this sort. 



The first general tables of this kind were published by 

 Mr. Mezger at Mannheim in 1778, and contained the cor- 

 rections of 352 stars. In 1807 Mr. Cagnoli extended these 

 tables to the corrections of 501 stars: and in the same year 

 Baron de Zach published at Gotha his Tabula spcciales Aber- 

 rationis et Nutatio?iis, which contained the corrections for 494 

 zodiacal stars. But, already these tables have nearly outlived 

 their utility. Independent of their very limited extent, the 

 elements from which they were deduced, have been super- 

 seded by others more agreeable to actual observation ; which 

 together with their exclusion of the solar nutation, and other 

 minute quantities which cannot safely be neglected in the pre- 

 sent state of astronomy, renders these tables of doubtful utility 

 to the practical astronomer. 



The number of zodiacal stars (without including the very mi- 

 nute ones) is considerably above a thousand: each of which may, 

 in the course of a revolution of the nodes, suffer an occultation 

 by the moon. These occultations are ascertained to be visible at 

 sea, even from the unsteady deck of a vessel under sail : and 

 afford the surest means of determining the longitude, provided 

 the position of the star could be well ascertained. In order 

 to furnish the corrections for each star, ten equations are re- 

 quisite, depending on the sine and cosine of given arcs; so 

 that it would require the computation of upwards of ten thou- 

 sand subsidiary tables in order to produce the necessary cor- 

 rections ; a labour so gigantic as to preclude all hope of seeing 

 it accomplished by the pen. By the help of the machine, 

 however, the manual labour vanishes, and the mental labour 

 is reduced to a very insignificant quantity. For, as I have 

 already stated, astronomical tables of every kind are reducible 

 to the same general mode of computation ; viz. , by the con- 

 tinual addition of certain constant quantities, whereby the 

 mean motions of the body may be determined ad vifinitum ; 

 and by the numerical computation of certain circular functions 

 for the correction of the same. The quantities depending on 

 these circular functions, let them arise from whatever source 



they 



