12 SIXTH REPORT. 1S36. 



pendulum equal to the 140,000dth part of an inch ; while the entire 

 suspending apparatus may be firmly screwed to the stone back of 

 the clock-case, and thus afford a very steady means of suspension, 

 quite independent of the clockwork. By this means an alteration 

 of the rate of the clock may be effected without stopping it ; and an 

 alteration to any required amount may be at once effected, after it 

 has been ascertained by experiment what change is made in the rate 

 by moving the micrometer index through a given number of the 

 degrees of its circle. 



A leaden tube, such as here described, can be very easily drawn 

 at any place where leaden tubes are manufactured, and is the cheapest 

 and best material for the purpose. It will be pro2)er to prepare 

 the deal rod by baking ; then by passing it through a cork in the 

 upper part of the receiver of an air pump, the ends of it can be 

 dipped into melted shell lac after the air has been extracted ; the 

 readmission of the air will drive the lac into the pores ; its outside 

 surface should also be made of the colour of lead by rubbing it with 

 black lead, a matter well known to be of considerable importance ; 

 and when the parts of the pendulum are put together, all may be 

 varnished. 



On the Importance of forming new Empirical Tables for finding the 

 Moon's Place. By J. W. Lubbock, Esq. 



During the last and the present century the tables for finding the 

 places of the moon and planets have been so much improved that 

 they may now be considered as sufliciently accurate for the purposes 

 of navigation. If therefore astronomical tables were to be viewed 

 merely with reference to the facilities which are obtained through 

 their means for long voyages, astronomers might be said to have ac- 

 complished all that was expected from them. Astronomers, how- 

 ever, have never been satisfied with this view of the question, but they 

 have constantly endeavoured to reach by calculation and theory the 

 same degree of accuracy as that which is obtained in fixed observa- 

 tories with the best instruments. This being the case much remains 

 to be accomplished. The expressions for the longitude and latitude 

 of the moon, to which I shall confine myself in the following re- 

 marks, have not yet arrived at the desired precision, although the 

 difficulties which remain to be overcome are by no means insur- 

 mountable. 



The most remarkable works on the theory of the moon, on account 

 of their extent, are those of MM. Damoiseau and Plana. 



M. Damoiseau's work, to which a prize was adjudged by the 

 French Institut, was published by that learned body in the Mdmoires 

 lies Savans Etrungers. M. Damoiseau has pushed to an almost in- 

 credible extent the approximation, following closely the method 

 given by Laplace in the Mt'c. Cel., and originally chosen by Clairaut. 

 But M. Damoiseau's calculations are so conducted and are presented 

 in such a shape, that it would be next to impossible to verify them, 

 nor do I think that such a verification will ever be attempted. 



