THE 



VOYAGE OF H.M.S. CHALLENGER, 



REPORT on some of the Physical Properties of Fresh Water and 

 of Sea- Water, by Professor P. G. Tait. 



INTRODUCTION, 



As I had taken advantage of the instruments employed for the determination of the 

 Pressure Errors of the Challenger Thermometers 1 to make some other physical 

 investigations at pressures of several hundred atmospheres, Dr. Murray requested me 

 to repeat on a larger scale such of these as have a bearing on the objects of the 

 Challenger's voyage. The results of the inquiry are given in the following paper. 

 The circumstances of the experiments, whether favourable to accuracy or not, are 

 detailed with a minuteness sufficient to show to what extent of approximation these 

 results may be trusted. My object has been rather to attempt to settle large questions 

 about which there exists great diversity of opinion, based upon irreconcilable experi- 

 mental results, than to attain a very high degree of accuracy. My apparatus was 

 thoroughly competent to effect the first, but could not without serious change (such as 

 greatly to affect its strength) have been made available for the second purpose. The 

 results of Grassi, Amaury and Descamps, Wertheim, Pagliani and Vincentini, &c, as 

 to the compressibility of water at low pressures, differ from one another in a most 

 distracting manner ; and the all but universal opinion at present seems to be that, for 

 at least five or six hundred atmospheres, there is little or no change in the com- 

 pressibility, the explicit statement of Perkins notwithstanding. My experiments have 

 all been made with a view to direct application in problems connected with the 

 Challenger work, and therefore at pressures of at least 150 atmospheres, so that I 

 have only incidentally and indirectly attacked the first of these questions ; but I hope 

 that no doubt can now remain as to the proper answer to the second. The study of 

 the compressibility of various strong solutions of common salt has, I believe, been 

 carried out for the first time under high pressures ; and the effect of pressure on the 

 maximum-density point of water has been approximated to by three different 

 experimental methods, one of which is direct. 



1 Narr. Chall. Exp., vol. ii., App. A., 1882. 



(PHYS. CHEM. CHALL. EXP. — PART IV. — 1888.) 1 



