22 Prof. Helmholtz on the Regelation of Ice. 



The three values of t, now to be called z + t, are found at p. 269 

 of the paper, and with the values of z give the equations 



^l ,/ -32-K/ 1 =-l ,/ -37, -2"-76 + / 2 =— 2"'22, 



-0' / 003 + jf 3 =— 0"053; 

 ... / 1= _0"05, * 2 =0"-54, t 3 = -0"-05. 



These are even smaller than those before obtained (I mean in 

 the paper), and show that no one of the three reference-stations 

 appears to be so situated (which might have been the case) as to 

 have a large local attraction. 



7. The three pairs of semiaxes deduced in the paper are, as 

 there stated, remarkably near to each other in value ; and there- 

 fore their mean, viz. 



0=20,926,189, and 6 = 20,855,316 feet, 



may be taken, as before announced, to be the mean semiaxes of 

 the earth. 



8. The speculations regarding the constitution of the earth's 

 crust, that it is such that we may conceive the elevations and 

 depressions of the surface to have been caused by unequal con- 

 traction of the materials of the crust, remain as before, and 

 appear to me well worthy of consideration. 



Calcutta, May 7, 1866. 



III. On the Regelation of Ice. 

 By H. Helmholtz. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



PROFESSOR HELMHOLTZ has forwarded to me the fol- 

 lowing Note, which forms an appendix to the translation 

 of his excellent lecture upon glaciers, recently published in the 

 Revue des Cours Scientifiques. You will, I doubt not, willingly 

 give it a place in the Philosophical Magazine. 



John Tyndall. 



To the Editor of the Revue des Cours Scientifiques. 



In reply to your question whether it is my desire to make 

 any remarks on the new and ingenious experiments of Professor 

 Tyndall, I would state that the results obtained with the swim- 

 ming ice certainly show that, by very feeble pressure, pieces of 

 ice may be caused rapidly to cling together. The pressures that 

 come into play in this case are partly the difference in specific 

 gravity between ice and water, and partly the capillary attrac- 



