Royal Society. 395 



interior of the earth is a dense fluid or semi-fluid (which for conve- 

 nience he calls lava), and that the exterior crust floats upon it. For, 

 he remarks, this crust cannot be supposed at any part to be very high 

 upwards (as in mountains), at least to any great horizontal extent, 

 unless there is a corresponding projection downwards into the lava. 

 Upon making a numerical calculation, even with the crust 100 miles 

 thick, it was shown that there would be such a tendency of the 

 table-land to crack and sink in the middle as no cohesion of rocks 

 can resist. He conceives that the state of the ground may be pro- 

 perly illustrated by a raft of timber floating on water : if one piece 

 of timber projects higher into air than the others, we are certain 

 that it also projects lower into water than the others. Assuming 

 this as established, then it is evident that the horizontal attraction 

 of a mountain-mass on a point at a considerable distance is nearly 

 evanescent, because the increase of attraction of the part which is 

 above the general level is sensibly neutralized by the deficiency of 

 attraction below it where the lighter crust displaces the heavier lava. 

 In like manner, the horizontal attraction of a ship or other floating 

 body is nothing. But the horizontal attraction upon a near point 

 on the earth's surface will not vanish, because the mountain which 

 produces the positive attraction is nearer than the lava-displacement 

 which produces the negative attraction : even here, however, the 

 efficient disturbing attraction will be much less than that computed 

 by considering the dimensions of the mountain only. 



Note to a paper entitled " Contributions to the Anatomy of the 

 Brachiopoda,"readJunel5,1854. ByThomasH.Huxley,Esq.,F.R.S. 



My attention having been called within the last two or three days, 

 to an error in my paper on the Anatomy of the Brachiopoda, 

 published in No. 5 of the Royal Society's Proceedings, I beg to be 

 allowed to take the earliest opportunity of correcting it. At p. Ill 

 of that paper the following paragraph will be found : — 



" In 1843, however, M. Vogt's elaborate Memoir on Lingula ap- 

 peared, in which the true complex structure of the 'heart' in this 

 genus was first explained and the plaited 'auricle' discriminated 

 from the 'ventricle;' and in 1845, Professor Owen, having appa- 

 rently been thus led to re-examine the circulatory organs of the Bra- 

 chiopoda," &c. &c. 



Now, in point of fact, though M. Vogt does describe and accu- 

 rately figure the structures called ' auricle' and ' ventricle' in Lin- 

 gula*, yet he has not only entirely omitted to perceive their con- 

 nexion, or to indicate the ' auricular' nature of the former, but he 

 expressly states that the so-called ' hearts' are " simple, delicate, pyri- 

 form sacs" (p. 13). 



I presume that my recollection of M. Vogt's figures was more 

 vivid than that of his text; for having been unable, notwithstanding 

 repeated endeavours, to re-obtain the memoir when writing my paper, 

 I felt justified in trusting to what seemed my very distinct recollection 



* Neue Denkschriften der allgemeinen Schweizerischen Gesellschaft fur die 

 gesamraten .Naturwissenschaften. Band VII. 



