lOfi Retrospective Gritieism. 



and constantly make excursions, as often as my very limited income per- 

 mits. With all your correspondent's opportunities, it is to be lamented 

 that he has hitherto published nothing respecting the economy or faculties 

 of animals of the least use to natural history. If he will take my humble 

 advice, before he publishes any thing else on hatching, he will provide him- 

 self with a good thermometer and a stop-watch. — ./. Rennie. Lee, Kent, 

 Nov. 3. 1831. [Mr. Waterton uses a watch in his observations : see p. 13.] 

 J%g5 wkeji covered and moistened more easily hatched (Vol. IV. p. 517.). 

 — Possessing but very little ornithological knowledge, and certainly with- 

 out having profited by the advice of Mr. Waterton, of journeying to the 

 East to consult the vizier of Sultan Mahmoud, learned in the language of 

 birds \ having, too, wandered amidst the bogs, rather in search of plants 

 than to study the habits of the feathered race, and therefore knowing 

 better the haunts of the pale pimpernel (^nag^llis tenella) and the ivy- 

 leaved campanula (Campanula /icderacea) than of dabchick or waterhen, 

 it may seem presumptuous in me to venture a suggestion respecting the 

 covering of their eggs by certain birds when leaving their nests. I know 

 not whether this habit is peculiar to water birds, or whether it is done by 

 all, or nearly all, of the Linnaean orders Grallae and yl'nseres, as in this 

 respect my knowledge is limited to the tame duck and the goose ; both of 

 which, particularly the latter, cover their eggs with the greatest care. May 

 not this be done rather to prevent the shells from becoming too much 

 hardened by exposure, than for the purpose of keeping them dry and warm, 

 as suggested by Mr. Rennie, in the passage of his work quoted by Mr. Wa- 

 terton ? I believe these shells are naturally hard and thick ; and it is a fact 

 well known to the rearers of these birds, that unless they have whilst 

 sitting free access to water, and can return at intervals with moistened 

 plumage to their nests, the embryo chicks find it impossible to break their 

 shelly enclosure, and consequently perish : to prevent which fatal cata- 

 strophe, water is sometimes sprinkled over the eggs. It would not, there- 

 fore, appear that moisture is injurious to the embryo ; but rather that, in the 

 case of some birds, at least, it is a requisite in the process of hatching. I 

 should, however, add, that when the eggs are thus sprinkled with water, it 

 is always tepid, perhaps to resemble, as nearly as possible, the degree of 

 heat it would imbibe from the bird whilst returning to its nest ; and that it 

 is also sometimes done, in very dry weather, to the eggs of the common 

 fowl when the process of incubation is nearly completed. Whether 

 doing so is, in all cases, the result of experience, and therefore right, or 

 whether it is only a vulgar error, I leave to others more capable than my- 

 self to determine. — C. P. Surrey, Kov. 1831. 



Sir J. Byerley's Theory, which accounts for Geological Phenomena by the 

 Precession of the Equinoxes. — Sir, I have seen a very specious paper in 

 Vol. IV. p. 308., by an old correspondent of mine. Sir J. Byerley, alto- 

 gether in error in its reference to any doctrine of mine, and equally so in 

 the doctrine which it assumes. 



It is alleged that I promulgated the idea, that the geological changes 

 arise from the precession of the equinoxes : but this I never taught ; for the 

 precession produces no physical effect, and no alteration of mechanical 

 power ; but merely carries back the nodes ; and, with reference to the equi- 

 noxes, causes the stars apparently to move forward, or in about 25,868 

 years to go round the ecliptic. This was not my idea : but I taught that 

 the geological changes arise from the advance of the line of apsides around 

 the ecliptic in about 20,930 years, because the extremities of that line con- 

 stitute the aphelion and perihelion points ; and as in these the difference 

 of distance is 3,000,000 of miles, so a difference of action and reaction 

 arises, sufficient to cause the mobile waters to respect the declination of 

 the perihelion, or point of greatest action. This theory I promulgated 

 at some length in the Monthly Magazine, so long since as 1813; and I 

 reprinted the same paper, as one of my Twelve Essays, in 1820. 



