186 



NOTE ON THE OBJECT OF THE SALT CONDITION OF THE SEA. 



[1855. 



light, a portion of which will fall upon the field of view. Sup- 

 pose we denote by the number 10 the additional illumination 

 of the field due to this cause ; then the brightness of the moon's 

 image will be 60 -)- 10 ^ 70, that of the surrounding image 

 of the corona 61 -|- 10 = 71. The excess, therefore, of the 

 brightneFS of the latter will be now only one-seventieth of the 

 general illumination, which, as we have seen before is not suf- 

 ficient to render the diiference perceptible. * On the other 

 hand, the chance of succeeding in the observation would have 

 been materially increased by placing a diaphragm with a small 

 aperture in front of the lens, thus protecting it from a great 

 portion of the extraneous rays. 51. Arago in his account of 

 the total eclipse of 1842, gives a remarkable instance of the 

 way in which the possibility of making this observation depends 

 on the character and condition of the telescope. He was observ- 

 ing at Perpignan, in company with M31. Mauvais and Laugrier, 

 and was himself at once struck with the phenomenon, which he 

 had not expected. He directed the attention of his fellow- 

 observers to it, but it was only with difiieulty that M. ^Mauvais 

 could detect it by means of his telescope, while M. Laugrier's 

 would not give it at all, though both those gentlemen saw it 

 distinctly in M. Arago's instrument. The telescopes used at 

 Prescott had been carefully cleaned ; but it is very diificult to 

 keep an object glass, and still more an object mirror, perfectly 

 free from all moisture. And, besides, it must be remembered, 

 that no amount of care in cleaning could have ensured the suc- 

 cess of the observation, if the object-glass or reflector was im- 

 perfectly polished. It is to be regretted that the precaution of 

 placing a diaphragm in front of the object-glass was omitted, 

 as this might very probably have rendered the phenomenon 

 visible. 



In conclusion, we may be permitted to obseiTe, that a par- 

 tial eclipse, however large, fails in exhibiting most of those 

 astonishing phenomena which render a total eclipse the most 

 striking of all celestial occurrences; and that in proportion as 

 the magnitude of the phenomena decreases, so does the difficulty 

 of observation increase. Considering also the shortness of the 

 period to which the manifestation of the phenomena is confined, 

 and the fewness of the opportunities that one person's lifetime 

 affords for such occurrences, if any disappointment be felt that 

 more was not accomplished on the present occasion, we would 

 refer to a remark made by Professor Smith of Edinburgh, on 



* This illustration is not strictly accurate, inasmuch as the eifect of 

 a film of dust or moisture on the object glass ivould be not only to in- 

 crease the general illumination of the field, but to diminish the direct 

 light received from the corona and the sky in the neighbourhood. It 

 ■will be seen, however, that if we take this into consideration, the effect 

 of the film in preventing our seeing the moon's disc projected on the 

 corona will be increased. Thus, if we denote by a, the general illu- 

 mination of the field, and by b, the additional light of the corona when 

 the object glass is clean, the ratio of the excess of brightness of the 

 image of the corona, to that of the portion of the field where the image of 



the moon is formed, will be _; when the general brightness of the 



a 

 field is increased by a quantity, e, in consequence of the interposition 



of a film on the object glass, the coiTesponding ratio will be 



a-f-c 

 the difference of the brightness remaining the same. This is obviously 

 less tUan the former ratio. If, now, we take into account the effect of 

 the film in diminishing the direct light, since the light of the corona 

 and the atmospheric illumination will be diminished in the same ratio, 

 we may write ma and mb for a and b, m being some proper fraction. 



Thus the ratio on which the visibility depends, will become 



ma-^c 



•which is less than ■ , and so, a fortiori, less than — 



a-\-c a 



the eclipse of 1851. He says, "on asking a worthy American, 

 who had come with his instruments from the other side of the 

 world, pointedly to observe the eclipse, what he had succeeded 

 in doing? He merely answered, with much quiet impressive- 

 ness, that if it was to be observed over again, he hoped that he 

 would then be able to do something, but as it was he had done 

 nothing; it had been too much for him." 



Note on the Object of the Salt Condition of the Sea. 



BY raor. chapman, u.niveksity college, tokonto. 



[^Communicated to the Canadian Institute, January 20, 1855.] 



For what beneficent purpose has the great Creator of all 

 things ordained that the sea shall be salt ? To this often 

 mooted question, no satisfactory answer has hitherto been 

 returned. So far as I can ascertain, the following suggestions 

 are all that have been proposed as yet in elucidation of the 

 subject : First, that the sea is salt, in order to preserve it in a 

 state of purity. Secondly, in order to render the water of 

 greater density, and consequently to impart a greater buoyancy 

 to bodies floating in it. And thirdly, in order to cause its 

 freezing point to be lower than that of fresh water, and hence 

 to preserve it from congelation to within a shorter distance of 

 the poles than would otherwise be the case. 



The first suggestion is scarcely tenable, because, without the 

 intervention of other conditions, the amount of saline matter 

 present in the sea is not sufficient to prevent the putrefaction 

 or decomposition of organic bodies. In many salt marshes and 

 on sheltered coasts, it is well known for instance, that after 

 heavy gales at sea, accumulations of sea-weed frequently collect 

 to such an extent as to occasion by their decomposition the 

 most injurious miasma. During calms, again, on low tropical 

 coasts, gaseous emanations arising from the decomposition of 

 animal matter in the sea, have often been remarked. In these 

 and other similar cases, it is to be borne in mind, however, 

 that the decomposing matters are present in unusual quantities 

 under the influence of peculiar or temporary causes. Under 

 ordinary conditions, it has now been satisfactorily shewn that 

 organic impurities — and these only can afiect the present ques- 

 tion — difiused through a vast body of moving water, whether 

 fresh or salt, become altogether lost, and with extreme 

 rapidity: so much so, indeed, as apparently to have called 

 forth a special agency to arrest the total destruction of 

 organised matter in its final oscillation between the or- 

 ganic and inorganic worlds. I allude to the myriads of 

 microscopic creatures which inhabit all waters, and whose 

 primary function is ably surmised by England's great ana- 

 tomist. Professor Owen, to be that of feeding upon, and 

 thus restoring to the living chain, the almost unorganised 

 matters diffused through their various zones of habitation. 

 Not only do we find these creatures in every stagnant pool, but 

 the sea itself teems with them in all their varied types. " The 

 application of the miscroscope," says Humboldt, "increases in 

 the most striking manner our impression of the rich luxuriance 

 of animal life in the ocean, and reveals to the astonished senses 

 a consciousness of the universality of life. In the oceanic 

 depths, far exceeding the height of our loftiest mountain chains, 

 every stratum of water is animated with polygastric sea-worms. 



