536 



SCIENTIFIC NEWS. 



[Nov. 23, 1888, 



of ^apettf, Hectureg, etc* 



ROYAL SOCIETY. 

 At the meeting on November 15th a paper " On the 

 Mechanical Conditions of a Swarm of Meteorites, and on 

 Theories of Cosmogony," was read by G. H. Darwin, 

 LL.D., F.R.S., Fellow of Trinity College and Plumian 

 Professor in the University of Cambridge. 



Mr. Lockyer's recent investigations have led the author 

 of this paper to make a suggestion for the reconciliation 

 of two apparently divergent theories of the origin of 

 planetary systems. 



According to the nebular hypothesis the solar system 

 originally consisted of a rotating globe of gas, which, as 

 it cooled, rotated faster, until it became so much flattened 

 that a ring of gas was detached from the equatorial region. 

 This ring then coalesced into a planet, and subsequently 

 other rings were formed, which in their turn became 

 planets. 



But notwithstanding the high probability that some 

 theory of the kind is true, the acceptance of the nebular 

 hypothesis presents great difficulties, and other specu- 

 lators on the origin of the planets have attributed their 

 existence to a gradual accretion of meteoric matter. 



The very essence of the nebular hypothesis is the con- 

 ception of fluid pressure, since without it the idea of a 

 rotating globe of gas becomes inapplicable. Now, at first 

 sight, the meteoric condition of matter seems absolutely 

 inconsistent with a fluid pressure exercised by one part 

 of the system on another. We thus seem driven either 

 to the absolute rejection of the nebular hypothesis, or to 

 deny that the meteoric condition was the immediate ante- 

 cedent of the sun and planets. 



The object then of this paper was to point out that by 

 a certain interpretation of the meteoric theory a recon- 

 ciliation may be obtained between these two orders of 

 ideas, and it may be held that the origin of stellar and 

 planetary systems is meteoric, whilst the conception of 

 fluid pressure is retained. 



It is now well established that a gas consists of minute 

 elastic molecules moving with great speed and continu- 

 ally coming into collision with one another. 



According to this so-called kinetic theory of gases, fluid 

 pressure is the average result of the impacts of mole- 

 cules. If we imagine the molecules magnified until of 

 the size of meteorites, their impacts will still, on a coarser 

 scale, give a quasi-fluid pressure. It is suggested then 

 that the fluid pressure essential to the nebular hypothesis 

 is, in fact, the resultant of countless impacts of meteorites. 



Problems involving gases could hardly be attacked with 

 success, if it were necessary to start from the beginning 

 and to consider the cannonade of molecules. But when 

 once it is proved that the kinetic theory wili give us a 

 gas which, in a space containing some millions of mole- 

 cules, obeys all the laws of an ideal non-molecular gas 

 filling all space, the molecules may be put out of sight 

 and the gas treated as a plenum. 



In the same way the difficulty of tracing the impacts 

 of meteorites in detail is insuperable, but if such impacts 

 give rise to a quasi-fluid pressure on a large scale, it may 

 become possible to trace out many results by treating an 

 ideal plenum. Laplace's hypothesis implies such a 

 plenum, and it was maintained by the author that this 

 plenum is merely the idealisation of the impacts of 

 meteorites. 



The paper contained an examination of the justifi- 

 ability of the suggestion, but the details are of too special 

 a character to admit of discussion here. The author 

 showed how the actual velocities are determinable of the 

 meteorites which made up the globular swarm from which 

 the sun originated, and he concludes that the collisions 

 between them must have occurred with sufficient fre- 

 quency to permit us to treat the swarm as in many 

 respects mechanically analogous with a gas, even at a time 

 when it was as widely diffused as the orbit of the planet 

 Neptune. 



Messrs. J. W. Largley, M.A., F.R.S., and H. M. 

 Fletcher, B.A., read a paper on the " Secretion of Saliva.' 

 The salivarj gland cells pour forth during secretion, 

 water containing in solution various salts and various 

 organic substances, the latter being in the case of the 

 sub-maxillary gland of the dog chiefly mucin. The ex- 

 periments given in the paper are in the main directed to 

 determining the conditions which affect the rate of 

 secretion of the different constituents of saliva, viz., 

 water, salts, and organic substance. 



It has previously been shown (Heidenham and others) 

 that when the chorda tympani — the secretory nerve 

 proceeding from the brain to the sub-maxillary gland — 

 is stimulated, the saliva alters its character the faster it 

 flows. The more rapidly secreted saliva contains a 

 higher percentage of organic substance and within limits a 

 higher percentage'of salts. Messrs. Langley and Fletcher 

 confirm the above, except as regards the limit to the in- 

 crease in the percentage of salts. They find that however 

 rapidly the saliva is flowing, and it can be made (by 

 stimulating the secretory nerve) to flow still faster, the 

 percentage of salts will increase. But each successive 

 equal increase in the rate of flow causes a less increase 

 in the percentage of salts in the saliva. Because of 

 this and because the rate of flow of saliva cannot be 

 indefinitely increased, the percentage of salts in saliva 

 never reaches the percentage of salts contained in blood 

 plasma. In the saliva from the sub-maxillary gland of the 

 dog, the maximum percentage of salts known to occur is 

 ■77, whilst blood-plasma usually contains "85 per cent, of 

 salts. Since there is reason to believer that the lymph 

 from which the glands secrete also contain about '85 

 per cent, of salts, it follows — and this is well known — 

 that the gland cells are able as it were to refuse to take- 

 up some part of the salts contained in lymph. The 

 behaviour of the sub-lingual gland of the dog is in strik- 

 ing contrast to the sub-maxillary gland. The sub- 

 lingual saliva contains about 1 per cent, of salts (Werther, 

 Langley, and Fletcher), i.e., it contains a higher percentage 

 of salts than that in blood-plasma. 



When pilocarpin — i-ioth to i-2oth of a grain — is 

 injected into the blood, a rapid secretion of saliva results. 

 Messrs. Langley and Fletcher find that when a mixture 

 of pilocarpin, lithium citrate, potassium iodide, and 

 potassium ferrocyanide is injected into the blood, lithium 

 can be detected in the first drops of the saliva secreted, 

 the iodide can be detected after the first six drops, and 

 is probably present in the earlier drops, whilst the ferro- 

 cyanide cannot be detected in the saliva at any stage of 

 secretion. 



It has been said above that the percentage of salts and 

 of organic substance increases as the rate of flow of 

 saliva increases. Messrs. Langley and Fletcher point 

 out that this is only the case under certain conditions. 

 The alterations in the character of the blood, or of the 

 normal blood flow through the gland, modify the percent 



