November 2, 1906.] 



SCIENCE. 



559 



rather than Lord Kelvin's, which has been 

 familiar to me for many years, 



1. The error which has arisen in judging 

 my paper proceeds from the habit of dealing 

 with common solids in the laboratory, and the 

 supposition that I am using the same method 

 in dealing with the effective rigidity of the 

 matter within the earth. The question as to 

 how the stresses are applied to a cubical ele- 

 ment does not need to be considered, for we 

 are not experimentally shearing or otherwise 

 deforming the elemental cubes of the earth 

 to get the resulting mean rigidity. Inside 

 the limit of pressure which gives the matter 

 the property of an elastic solid, the simple 

 fact is that there is an effective rigidity in 

 spite of the high temperature. Pressure 

 operating through the agency of molecular 

 forces, therefore, is the sole cause of the ef- 

 fective rigidity and I have taken the effect- 

 ive rigidity everywhere proportional to the 

 pressure, which is a perfectly legitimate hy- 

 pothesis. If others wish to adopt a different 

 hypothesis, they are at liberty to do so. The 

 present hypothesis is satisfactory on theoret- 

 ical grounds, and apparently confirmed by the 

 numerical calculations given in Astronomische 

 Nachrichten, No. 4,104. 



2. It may be well to observe that it is a 

 matter of the utmost indifference to me how 

 the elemental cube may be distorted, or 

 whether it be distorted at all. I am not de- 

 termining coefficients of rigidity for the dif- 

 ferent elements within the earth. For my 

 purpose of calculating the earth's mean rigid- 

 ity, it is sufficient to have something which 

 these rigidity moduluses would he propor- 

 tional to if they could he determined, and 

 that is the pressure, as calculated from the 

 theory of gravity and Laplace's law of density. 



3. The rigidity of ordinary solids may be 

 expressed in atmospheres; and in dealing with 

 bodies made rigid by pressure, it is convenient 

 to employ the same measure, since this enables 

 us to compare the rigidity of a cold solid to 

 that of a hot body made rigid by confining 

 pressure. 



4. There is an old saying that 'facts are 

 stubborn things.' Such, it seems to me, are 



the numerical results obtained in my paper, 

 by processes of entire mathematical rigor. 

 I calculate that the rigidity of the earth will 

 lie between 750,000 and 1,000,000 atmospheres. 

 In finding this lower limit, the effect of the 

 earth's crust is neglected, and there is, more- 

 over, some slight defect in the gravitational 

 method near the surface even in the case of 

 encrusted bodies. In the case of gaseous 

 bodies, the outermost layers can hardly be 

 regarded as having the properties of an elastic 

 solid, and hence the integration for the mean 

 pressure should stop before we reach the sur- 

 face. But as we do not know at what depth 

 to stop, I took the mean pressure of the entire 

 planet as giving its most characteristic prop- 

 erty. 



From these considerations I believe that 

 those who study the paper in Astronomische 

 Nachrichten, No. 4,104, will agree that the 

 points raised relate to the experimental de- 

 termination of moduluses of rigidity, and not 

 to the rigidity of the earth and other planets, 

 which are found by theoretical methods fully 

 explained in the paper itself. 



T. J. J. See. 



U. S. Naval Obsebvatoby, 

 Mabe Island, Calif., 

 October 3, 1906. 



anatomic nomenclature: an open letter to 

 professor llewellys f. barker. 



Dear Dr. BarJcer: Through absence from 

 home I have but just received from the pub- 

 lishers your " A Description of the Basle 

 Anatomical Nomenclature [B N A], advance 

 sheets from Dr. Llewellys F. Barker's forth- 

 coming book, ' Anatomical Terminology.' " I 

 rejoice that the subject is to be so fully and 

 ably presented to English-speaking teachers 

 and students of anatomy. Although many of 

 the terms of the [B N A] are not preferred 

 by me, yet — pending the expected eventual 

 general acceptance of my own — I should hail 

 their provisional adoption to the exclusion of 

 their numerous even less worthy synonyms, 

 as enabling me to replace a ' shot-gun policy ' 

 by rifle-practise. 



I take for granted that the paragraph on 

 page 5 was intended to represent justly my 



