March 15, 1877] 



NATURE 



437 



During our expedition I therefore considered it a very im- 

 portant object to examine closely the distribution of the " aat " in 

 the tract of sea over which we sailed. For this purpose the sea 

 was examined almost daily, often several times a day, by the 

 help of a surface-net. The results of these examinations com- 

 pletely confirmed my previous view on this point. During the 

 whole passage from Norway to the Faeroe Islands, the sea was 

 found everywhere filled with enormous masses of the so-called 

 " red aat " (almost exclusively Calanus fininarchicus) which, as 

 is well known, forms the food best liked by the herring, and, 

 what deserves to be remarked, the quantity of this "aat" 

 appears "to increase with the distance from the coast, being 

 greatest at a distance of about twenty Norwegian (140 English) 

 miles. Besides the " red aat " we also observed farther out to 

 sea, great quantities of another pretty blue sort of " aat '' {Pon- 

 tcUa Patersonii), which appears to belong more to the Atlantic 

 Ocean, and which, to distinguish it from the other, might be 

 called the "mackerel aat," as it probably forms the principal 

 food of the mackerel at those seasons of the year when this fish 

 is not in the neighbourhood of the coast. This "aat" also 

 shows itself sometimes, particularly during great takes of herring 

 in summer, among the ' ' red aat " close to the coast. When we 

 went northwards from the Fseroe Islands toward Iceland, it was 

 remarkable that the "aat" almost entirely disappeared from 

 the sea. At the same lime the sea had assumed a very different 

 colour. While during the whole passage from Norway to the 

 Fseroe Islands it had been a deep blue, it was now [a light, 

 dirty, greyish-green. This peculiar circumstance, for which I 

 cannot yet account, but in which a peculiar relation of the 

 ocean currents certainly plays a considerable part, appears to 

 stand in close connection with the occurrence of ' ' aat, " and will 

 be the subject of careful researches during our next expedition. 

 I had a very convenient opportunity of observing this pheno- 

 menon from my cabin, the li^ht of which was almost on a level 

 with the sea. When, by the pitching of the vessel, the glass 

 was washed over, the whole cabin was clearly illuminated with 

 a very beautiful, intense dark blue light, and I have often, when, 

 after my work was ended, I was taking a little rest in my cabin, 

 been greatly delighted with this phenomenon, which so strikingly 

 reminded me of my stay in the south the preceding winter, and 

 my ever-memorable visit to the blue grotto at Capri. Now, 

 on the contrary, the illumination was quite different, namely, 

 light greenish. This colour remained constant so long as we 

 were in the navigable water near Iceland, and the sea was 

 everywhere, as has been stated, almost completely free from 

 "aat." The previously-observed state of things recurred first 

 when we, on our return voyage, approached the coast of Norway. 

 The water resumed its beautilul blue colour, and the sea swarmed 

 with "aat." I cannot help supposing that the conditions 

 observed during our expedition is not always the same, as 

 several recent accounts state that the sea about Iceland is 

 specially rich in "aat." It appears as if the constant westerly 

 storm, which we had to put up with during our expe- 

 dition, in combination with the strong up-going current, had 

 had a disturbing action, and forced the mass of "aat" 

 farther in towards the Norwegian coast. If this should 

 in fact be the case, a supposition which in the mean time with 

 the little experience we have yet had on the point can scarcely 

 be supported with full evidence, there may be seen in this (if 

 the above-mentioned theory of mine with reference to the migra- 

 tions of the herring be accepted) a good omen of the improve- 

 ment of the spring herring fishery in the near future. That the 

 herring is where the herring food (the "aat") is, I consider a 

 settled point. Although we unfortunately had no opportunity of 

 directly establishing the presence of herring by the help of our 

 nets, there were not wanting the best signs of it at the points 

 where the "aat" was most numerous. Not a few whales (both 

 sildehval, Physalus antiquormn, and staurhyrning, Orca gla- 

 diator) were observed at such places, as well as large numbers of 

 birds (chiefly kittiwakes), and, at a considerable distance from 

 the coast at stations 75 ^ and 76 ^, there were large brown spots 

 in the sea, like extensive sea-weed fields, but which on a closer 

 examination were found to be enormous masses of " aat" closely 

 packed together, on which the fulmar petrels (Jirocellaria gla- 

 cialis), our constant companions during our excursion, feasted to 

 their heart's delight. That these enormous " aat " masses could 

 not be packed together here by pure accident is evident, and 

 that the current alone should be able to do this here far out in 



« Station 75, lat. 64° 47' 2" ; long. 7° 13' E. from Greenwich. 

 ' St.ition 76, lat. 64° 47' 4'' ; long. 7° 3' 6" E. from Greenwich. 



the open sea I cannot believe. I am rather of opinion that 

 the herring shoals have driven this " aat," together in the same 

 way as may often be observed in the case of coal-fish, and that 

 there, under these brown spots on the sea, there were enormous 

 shoals of herring (sildebjer^e). 



I am much disappointed that circumstances did not permit us 

 to use our nets here. We might have been able in this way 

 readily to establish the occurrence of the herring far out at sea. 

 It is to be hoped in the mean time that in our next expedition we 

 shall be more fortunate in the weather, and we shall then put this 

 herring question in the first rank, the rather as we shall be then 

 farther north or nearer the waters, which, in my opinion, are 

 the proper home of spring herrings {vaarsilden) and the great 

 herrings {storsildens). 



OUR ASTRONOMICAL COLUMN 



The Suspected Intra-Mercurial Planet.— M. Le- 

 verrier, in a circular addressed to astronomers, has again directed 

 attention to the importance of close and frequent observations of 

 the sun's disc, on March 21, 22, and 23, but especially on the inter, 

 mediate date, with the view to detect the small planet, which he 

 assumes to have been already observed in transit on six occasions, 

 and which there would appear to be just a possibility, may be 

 again projected upon the face of the sun at this time. In his 

 reasoning upon this subject, M. Leverrier adopts for the place of 

 the node, the value he had deduced from the well-known obser- 

 vations of Dr. Lescarbault on March 26, 1859, but the uncer- 

 tainty attaching to the result renders it impossible to pronounce 

 definitively on the occurrence of a transit in the present month. 



The six observations to which reference is made above are 

 those of Fritsch, at Quedlinburg, October 10, 1802 ; Stark, at 

 Augsburg, October 9, 1819 ; Decuppis, at Rome, October 2, 

 1839 ; Sidebotham, at Manchester, March 12, 1849 ; Lescar- 

 bault, at Orgeres, March 26, 1859 ; Lummis, at Manchester, 

 March 20, 1862. 



Attributing these observations to the passage of a single planet 

 across the sun's disc, he found a formula for the heliocentric 

 longitude at any time, in which an indeterminate entered, allow, 

 ing of several solutions of the problem of finding the period of 

 revolution, and hence the mean distance of the body from the 

 sun. Two of the solutions appear to possess equal precision in 

 the representation of the observations ; in the first, the time of 

 revolution is found to be 33*02 days, and the mean distance from 

 the sun o •201, that of the earth being taken as unity: in the 

 second solution the length of the revolution is 27'96 days, and 

 the mean distance o"i8o. Whichever period we adopt, we find 

 from M. Leverrier's formula that the suspected planet should 

 be in conjunction with the sun on March 22, astronomical 

 reckoning, for the meridian of Greenwich, though to decide 

 definitively as to the passage or otherwise of a planet across the 

 sun's disc at this time, it will be necessary to examine it not 

 only throughout the whole of the corresponding revolution of 

 the earth upon her axis, but owing to uncertainty in the data for 

 prediction, during the twenty-four hours preceding and following, 

 or as already stated, on March 21, 22, and 23. 



It is difficult to understand how six observers, without, as M. 

 Leverrier remarks, any relation with each other, nor any know- 

 ledge of the periods under discussion, can have fallen by chance 

 upon six exact epochs of a phenomenon explicable by the 

 motion of a single planet. Though suspicion has attached in 

 the minds of some astronomers to one or two of the observa- 

 tions to which we have referred, the fact pointed out by the 

 illustrious French astronomer does appear very strongly confirm- 

 ative of their reality. At any rate, the existence or otherwise of 

 such a body may be decided by systematic examination of the 

 sun's disc, near the calculated epochs of conjunction, within 

 the assumed transit-limits ; but it so happens that after the 

 present month there is very little probability of ,a transit 



