March 31, 192 1] 



NATURE 



139 



If, on the other hand, a suspended particle of 

 dimensions double that of a molecule of starch be 

 considered, the fraction of the hemisphere ASB (Fig. 2) 

 which would be occupied by the suspended particle 

 would be five-eighths, and would include all that part 

 of it where any effective component in the direction 

 CS could be developed, so that the resultant acting 

 on a molecule of the surrounding liquid at C in this 

 case would be considerably more than five-eighths of 

 the full internal pressure at a plane surface. 



From such considerations it is clear that in passing 

 from molecules of the dimensions estimated for those 

 that give true solutions to molecules of the size that 

 is compatible only with colloidal solution, if the rela- 

 tion between these dimensions and the radius of the 

 sphere of molecular attraction is such as has been 

 presented, a very great change in the behaviour of a 

 solvent such as water must be observed. Considering 

 only, as has been done in this letter, the relations 

 between the molecules of solvent, the force tending 

 to withdraw these molecules from the surface of 

 molecules of solute will be found to increase eight- 

 thousandfold. The large molecules must be far more 

 unstably dispersed than the small. As soon as they 

 come within a distance of each other which is less 

 .than the radius of attraction for the solvent, they 

 will be forced together by the internal pressure of the 

 solvent. 



The force tending to remove a molecule of solvent 

 from the surface of a particle 100 A. in diameter>f 

 say = 75 per cent, of the internal pressure at a plane 

 surface ; a starch molecule 50 A. in diameter>J 

 say ===33 per cent. ; a molecule 25 A. in diameter>i/32 

 say = 5 per cent.; a CO, molecule 25 A. in dia- 

 meter> 1/32000 say = 0-005 P^^" cent. 



In this consideration of the conditions obtaining in 

 solutions no account obviously has been taken of anv 

 forces except those in play between the molecules of 

 solvent. The supposition of such forces carries with 

 it the supposition also of similar forces acting between 

 molecules of solute, and especially, too, between them 

 and the molecules of solvent. When there is no at- 

 traction between solute and solvent, even the small 

 residuum of unbalanced internal pressure which a 

 particle leaves free to act on the molecules of the 

 dispersing medium when its dimensions are as small 

 as those assigned to the molecule of carbon dioxide 

 must result in its joining up with others of its kind — 

 in fact, in its being insoluble. The difFicultv that 

 such considerations taken bv themselves leave un- 

 touched is the difference between the finite degrees of 

 solubility peculiar to each kind of substance capable 

 of dissolving in a solvent. . J. B. Leathes. 



The University, SheflReld. 



Oceanographic Research in the British Empire. 



In the interesting leading article in Nature of 

 March 10, and in the discussion which preceded it, 

 one method of conducting oceanographic research 

 appears to have been practically ignored. We mean 

 its encouragement in permanent institutions and by 

 continued marine surveys in the diverse parts of the 

 British Empire. You have rightly laid stress on the 

 importance of intensive study in particular localities, 

 but we doubt whether research of the kind can be 

 carried out in a satisfactory manner by parties de- 

 tached for limited periods of time from an expedition 

 of world-wide scope. There is nothing that has struck 

 us more in our own work on the Indian seas and 

 lagoons than the importance of returning' again and 

 again to the same place to investigate special 

 problems. For example, in the investigation of the 

 fauna of the Chilka Lake, a small offshoot of the 



NO. 2683, VOL. 107] 



Bay of Bengal, now being completed by the Zoo- 

 logical Survey of India, the true character of the fauna 

 is being elucidated only by returning year after year 

 and month after month to the same hunting-grounds ; 

 and it is not only the fauna to which this applies, for 

 we find that the hydrography also must be studied 

 again and again in years of different climatic condi- 

 tions and at all seasons. The Chilka Lake is only a 

 minute, almost isolated, fragment of the ocean, but 

 in order to obtain a solid basis for the working out 

 of any oceanographic problem recurrence is necessary, 

 not only because conditions change from time to time 

 —and in many parts of the ocean they change, so far 

 as we know, very little — but also because detailed 

 work on results obtained in the field inevitably opens 

 new vistas, suggests unsuspected sources of error, and 

 reveals paths that ought to be followed out. 



We would suggest, therefore, the possibility of 

 giving further encouragement to local oceanographic 

 investigations. Such investigations have hitherto been 

 very largely, though by no means exclusively, of a 

 faunistic nature; for example, Dr. Gilchrist's work 

 on the seas of Africa, that of the Australian Fisheries 

 Department, and last, but not least, that of the 

 R.I. M.S. Investigator in Indian seas. There is no 

 reason, however, except the lack of physicists, to use 

 the term in a broad sense, why this should be so, and 

 even zoology, not to mention botany, still offers an 

 unlimited scope for oceanographers. War has inter- 

 fered with the work of the Investigator, but we have 

 every reason to hope that her scier-tific researches will 

 shortly be resumed under conditions more satisfactory 

 than ever before, and that for at least one month 

 every year the work of the ship will be devoted to 

 purely scientific research. The Madras Fisheries 

 Department already possesses a small marine labora- 

 tory in the Gulf of Manaar, and we hope that the 

 Zoological Survey of India will shortly be in a position 

 to open a larger one in the Andaman Islands, the 

 seas round which, perhaps, offer as good oppor- 

 tunities for oceanographic investigations of all kinds 

 as any seas in the world. The interest of the Govern- 

 ment of India in work of the kind is proved bv the 

 fact that the post of Surgeon-Naturalist to the Marine 

 Survey of India has been in existence since 1875. 

 Shortly before the war the trustees of the Indian 

 Museum, with the approval of the Government, con- 

 sulted the leading marine biologists throughout the 

 world as to the advisability of granting increased 

 facilities to the Surgeon-Naturalist, and the Govern- 

 ment accepted the practically unanimous verdict of 

 the experts bv voting additional grants, etc. It has 

 only been the war that has interfered with Its 

 .<^enerous proposals. We are not acquainted with 

 details as to the encouragement given to oceano- 

 graphic research in the Dominions, but the instances 

 we have already cited are sufficient to prove that it 

 has not entirely lacked sympathy, even if only from 

 a strictly practical point of view. 



Would It not. perhaps, be more feasible to approach 

 the different Governments of the British Empire, 

 which abuts on the seas of all the world, to organise, 

 with the aid of the experts in their employment, 

 separate but co-ordinate research rather than to 

 attempt to set on foot a single colossal expedition 

 the cost of which Is admitted at present to be pro- 

 hibitive, while its course could not be permanent, or, 

 indeed, extend for more than a comparatively few 

 years ? 



N. Annandai.e. 

 Director. Zoological Survey of India. 



R. B. Seymour Sewell, 



Surgeon-Naturalist to the Marine Survey 



of India. 



Royal Societies' Club, St. James's Street. 



