210 Linnaean Society. 



much increased, that magnetism is a quality not essentially distinct 

 from electricity. 



Feb. 3. A paper was read On the Lunar Theory. Communicated 

 by the Rev. Dr. Lardner, F.R.S. 



The subject treated of in this paper is introduced by a review of the 

 labours of Clairaut, Euler, D'Alembert, and Thomas Simpson. The 

 theories of these eminent men, the author remarks, were very defici- 

 cient in accuracy, and were not at all adequate, without correction 

 from observation, to the construction of tables. They could serve 

 only to point out the arguments of the equations, and not all even of 

 these. The inequalities of the moon's motion are investigated by ap- 

 proximating processes, which lead to results more or less accurate, 

 according as the approximations are carried to a greater or less ex- 

 tent. The writers above mentioned had contented themselves with 

 short and easy approximations j and though they had accomplished 

 much, had yet left much more to be done. Subsequently to these, 

 Mayer published an elaborate theory of the moon j but his coefficients 

 required much correction, the results of his computations being in 

 some cases found to differ very widely from observation. A much 

 greater degree of accuracy was attained by Laplace, who bestowed 

 particular attention to the influence of minute quantities, in every 

 part of his theory. In the present paper the author has endeavoured 

 to introduce further improvements into the lunar theory, by carrying 

 the approximations considerably further than had hitherto been ac- 

 complished. 



In the solutions of the problem given by former mathematicians, 

 the chief obstacle to the attainment of accuracy was the extreme 

 length and labour of the necessary computations. Another object, 

 therefore, which the author has had in view, is to facilitate these com- 

 putations, and render them less laborious. This he endeavours to 

 effect by the employment of certain artifices, by which the multiplicity 

 of small terms will, with their coefficients, be reduced within a prac- 

 ticable compass, and their numerical computation rendered less ap- 

 palling. 



The coefficient of the equation depending on the moon's distance 

 from the sun, affords the means of calculating the sun's horizontal 

 parallax. For this purpose Laplace has computed this coefficient 

 with greater accuracy than the rest j and he makes the sun's pa- 

 rallax nearly 9". The author's theory gives it little more than 8J", 

 which is very near the mean of the various results obtained by the 

 observation of transits. He thinks that there is, therefore, great 

 reason to conclude that its true value is about this quantity. 



LINN.EAN SOCIETY. 



Feb. 1. A. B. Lambert, Esq. in the chair. 



A communication from John Blackwall, Esq. F.L.S. was read, in- 

 titled Remarks on the Pulvilli of Insects. In this paper the writer con- 

 troverts the statement of Dr. Derlmm in his Physico-Theology, sup- 

 ported by Sir E. Home, and generally adopted by naturalists, that the 

 feet of flies and other insects are furnished with " skinny palms," 

 which enable them to stick on glass, c, by means of the pressure of 



