28 REPORT — 1855. 



their values, as well as that of P, are only wanted to be known to the nearest 

 minute. The angle | given by formula (c) or (c)', ought to be taken lesser or 

 greater than 180", according as the values of the numerators will be positive or 

 negative. 



Note II. — The fluxions or derivates m , ri ; m', ri' of first and second order, 

 may be valued by employing the corresponding horary motions given by tables, 

 which would be more analytical, but in practice it will be found more convenient 

 to take out from the ' Nautical Almanac,' or from other sources, for an hour before, 

 the instant of the observation, for this instant, and for an hour after, the necessary 

 elements for computing three successive values, w— i, m, in, and « — i, n, Wj, and to 

 make 



>n,— TO+(m — m_i) Wi — M-f-(n— w-,) 

 = ra 2 , «'= ^ 



1 nji— m — {yn — m-^\ \ n^— n — («. — «-.) 

 — m — — , — n = = 



2 2 ' 2 2 



I subjoin here some faults of printing discovered in Dr. Pearson's work : — 

 At page 634, Une 13, read ^?ace instead of plane. 

 At page 635, line 10, the formulae must be 



m = cos B cos (a — A), n = sin h cos B cos (a — A) — cos b sin B. 

 At page 635, line 10, read 34' 57" instead of 3' 51". 



Remarks on the Chronology of the Formations of the Moon, 

 By Professor Nichol, LL.D., Observatory, Glasgow. 



Prof. Nichol stated, that, through the munificence of the Marquis of Breadalbane, 

 he had been enabled to bring to bear on the delicate inquiries, whose commencement 

 he intended to explain, a very great, if not a fully adequate amount of telescopic 

 power. A speculum of twenty-one inches, originally made by the late Mr. 

 Raraage with the impracticable focal length oi fifty -five feet, had, at the expense of 

 that noble Lord, been re-ground, polished, mounted as an equatoreal, and placed in 

 the Glasgow Observatory, in its best state, only about six weeks ago. Prof. Nichol 

 showed some lunar photographs, which indicated the great light with which the 

 telescope endowed its focal images, and entered on other details as to its definition. 

 The object of the present paper is the reverse of speculative. It aims to recall from 

 mere speculation, to the road towards positive inquiry, all observers of the lunar 

 surface. To our satellite hitherto those very ideas have been applied, which confused 

 the whole early epochs of our terrestrial geology, the notion, viz. that its surface is a 

 chaos, the result of primary, sudden, short-lived and lawless convulsion. We do not 

 now connect the conception of irregularity with the history of the earth : — it is the 

 triumph of science to have analysed that apparent chaos, and discerned order through 

 it all. The mode by which this has been accomplished, it is well known, has 

 been the arrangement of our terrene mountains according to their relation to time : 

 their relative ages determined, the course of our world seemed smooth and harmo- 

 nious, like the advance of any other great organization. Ought we not then to attempt 

 to apply a similar mode of classification to the formations in the moon, — hoping to 

 discern there also a course of development, and no confusion of manifestation of 

 irregular convulsion ? Prof. Nichol then attempted to point out that there appeared 

 a practical and positive mode by which such classification might be effected. It 

 could not, in so far as he yet had discerned, be accomplished by tracing, as we had 

 done on earth, relations between lunar upheavals and stratified rocks ; but another 

 principle was quite as decisive in the information it gave, viz. the intersection of dis- 

 locations. There are clear marks of dislocation in the moon ; nay, the surface of 

 our satellite is overspread with them. These are the rays of light, or rather bright 

 rays, that flow from almost all the great craters as their centres, and are also found 

 where craters do not at present appear. Whatever the substance of this highly 

 reflecting matter, it is evidently no superficial layer or stream, like lava, but extends 



