Barometric Measurements rf Heights. 235 



mer note states, that in order to obtain the perturbations of the 

 orbit with great exactness, it was necessary to carry the calcula- 

 tion to hundreds of seconds, which have been given in the Tables : 

 "Mais on pourra pour I'usage ordinaire se contenter des dixiemes, 

 et retrancher en mcme terns un cli'iffre des tons les argumens." 



I am at a loss how to interpret this cutting off ajigure from 

 all the argtiments. Had it stated, y;o/w the e(jilations, I should 

 have concluded that, if the calculations were carried to two places 

 of decimals, the last figure should be suppressed. But how a 

 figure is to be cut off from all the arguments of longitude, ex- 

 cept as is usual when the argument exceeds the extent of the 

 Table, I do not see. The same difliculty occurs page 256, where 

 it is observed, " La Table suivante donne les perturbations du 

 rayon vectenr en dix-millioniemes ; c'est pourquoi, aprSs en 

 avoir fait la somme, il faudra en retrancher le dernier chifl're, le 

 rayon vectenr n'etant donnc qu'en niillioniemes." Now the ex- 

 tent of the Table of Equations of the Rad. Vect. to Argum. I. is 

 10000. I conceive therefore that the meaning of this note is, 

 that when the equation exceeds four figures, the la^^t (to the left 

 hand) is to be suppressed. 1 do not know how it can be inter- 

 preted otherwise with propriety. 



If any gentleman who has satisfied himself as to these difficul- 

 ties, will be kind enough to communicate his sentiments to me 

 through your Magazine, I shall esteem it a favour, and feel greatly 

 obliged to him, and to you. 



Permit me to ask if the Tables of Ceres, Pallas, and Juno, are 

 printed ? Bode gives the positions of the two latter occasionally, 

 but I am ignorant whether the Tables are in private hands, or 

 not. 



Mardi7, 1S21. Z.N. 



BAROMETTIIC MEASUREMENTS OF HEIGHTS. 



Rowland Street, fWi March, 1 S21 . 

 Sm, — I have been much gratified by observing the zeal with 

 which the efforts oi Mr. Bevm have been seconded by your Cor- 

 rr pondents, in communicating their Barometric 01)servations, 

 carefully made in defined situations, on the se':ond Monday in 

 f(i h Month, at the hours S, 0, 10, 11, and 12 of the forenoon ; 

 and I sincerely hope and beg to request, that they will furtlier 

 persevere ; and also that other gentlemen resident on the differ- 

 ent Coasts of our Island will imitate their praiseworthy example; 

 carefully connecting their place of observation, by a Spirit Le- 

 velling, with the low and high lualer marks, of their respective 

 neighbourhoods. These maritime observations are of the utmost 

 consef[ucnce to be simultaneously made with others at various in- 

 land points, towards obtaining nearly aproximating heights of 



G g 2 the 



