CORRESP ONDENCE. 



743 



CORRESPONDENCE. 



RETARDATION OF THE EARTH'S ROTA- 

 TION. 



To the Editor of the Popular Science Monthly : 



SIR : In the work entitled " Correlation 

 and Conservation of Forces," edited by 

 you, is an article on " Celestial Dynamics," 

 by Dr. J. B. Mayer, in which is considered 

 the subject of the diminution of the velocity 

 of the rotation of the earth, in consequence 

 of the retarding influence of the tidal wave. 

 In the course of this article it is stated 

 (page 297) that " theory and experience 

 agree in the result that the influence of the 

 moon on the rotating earth causes a mo- 

 tion of transition from east to west in both 

 atmosphere and ocean," and that " this mo- 

 tion must continually diminish the rotatory 

 effect of the earth, for want of an opposite 

 and compensating influence." 



The result of the retarding force of the 

 waters on the axial motion of the earth is 

 stated, by Dr. Mayer, to be the lengthening 

 of the day -fa of a second in 2,500 years ; 

 and, further, that this retarding force will 

 eventually diminish and exhaust the earth's 

 rotatory motion. 



The theory of Laplace, that opposite 

 aerial currents are, as to their effects upon 

 the rotation of the globe, as = 0, and gen- 

 erally, that there are no forces at work in 

 Nature which do not in Nature find their 

 compensating opposites, is held by Dr. 

 Mayer not to be applicable to the effect of 

 this tidal translation of waters. Neverthe- 

 less, he proceeds to demonstrate, in the 

 article on " The Earth's Interior Heat," 

 that the decrease of temperature has been 

 far too great, in the last 2,500 years, to 

 have been without sensible effect in accel- 

 erating the velocity of the earth's axial 

 motion. It is there shown that the loss 

 of heat and consequent contraction of the 

 earth's surface, in the time above men- 

 tioned, must have had the effect of accel- 

 erating the earth's rotatory motion to the 

 extent of counteracting the retarding move- 

 ment of the tides. 



Now, if the results of these forces are 



equal one to the other, the day remains 

 constant, and the law of Laplace would 

 seem to apply as perfectly in this case as 

 in that of opposing aerial currents. 



T. H. S. 

 Cheyenne, W. T., February 16, 1875. 



THE NEST AND EGGS OF THE THISTLE- 

 BIRD. 

 To the Editor of the Popular Science Monthly : 



The yellow-bird (Chrysomitris tristis) is 

 exceedingly abundant throughout New Jer- 

 sey during eight months of the year, and 

 not at all rare during the winter, when it is 

 seeu mostly in loose flocks. For several 

 years I have been perfectly familiar with 

 its manner of nesting, and the appearance 

 of the eggs, etc., and I can give my testi- 

 mony to the correctness of the statements 

 of Wilson, who says these birds cover the 

 nest " on the outside with pieces of lichen, 

 which they find on the trees and fences." 

 In looking over the first volume of the 

 American Naturalist, p. 115, I noticed a 

 statement, made by Dr. T. M. Brewer, that 

 he " never saw one that was ever covered on 

 the outside with lichen;" and, in "North 

 American Birds," vol. i., p. 474, he de- 

 scribes a nest from Wisconsin as typical, 

 which, on the exterior, was solely "fine 

 vegetable fibres." Here, in New Jersey, 

 and it was from New Jersey nests (or Penn- 

 sylvania) that Wilson took his description, 

 the nests are invariably lichen-covered. I 

 believe I am justified in using so positive a 

 term. I know that here, also, two broods 

 are raised. So much for the nests. 



I have seen many sets of eggs, probably 

 200, within ten years, and I know tht.it 

 splotches of yellowish-brown, and occasion- 

 ally purple, are common on the larger end 

 of the egg ; not the rule, perhaps, but com- 

 mon, i. e., perhaps thirty per cent, of the 

 eggs laid. 



Charles C. Abbott, M. D. 



Trenton, N. J., February 16, 1875. 



