434 



JVa ture 



[Febkuauv io, 1910 



all the large fresh-water systems of South America, 

 western North America, and West Africa is due to 

 the fact that the temperature in the deeper layers of 

 the adjacent seas is too low to admit of the propaga- 

 tion." Incidentally, an explanation is afforded of the 

 hitherto puzzling lack of success which attended the 

 transplantation of eels from the eastern to the Pacific 

 States by the U.S.A. Fish Commission in 1874 and 

 other years. The eels themselves flourished in their 

 new surroundings, but the Pacific Ocean afforded no 

 place for successful reproduction. 



Oceanic hydrography has thus supplied the indis- 

 pensable key to the elucidation of a point in the 

 biology of a species which is universally regarded as 

 a fresh-water form. More strictly, however, AngidUa 

 vulgaris may be considered as an oceanic species 

 which has acquired the habit of migrating to fresh 

 water for food and protection. 



After all, the most interesting feature of this work 

 is that it deals with an extreme case of the problem 

 of the relationship between physical environment and 

 fish propagation, a most important question in con- 

 nection with the economic aspect of the fish supply. 

 Dr. Schmidt has contributed pioneer work of great 

 value towards the understanding of these phenomena 

 in regard to other species besides the eel. We may 

 mention, for example, his research upon the plaice and 

 cod in Icelandic waters, where he has shown by 

 marking experiments that a regular spawning 

 migration takes place into the warmer Atlantic water 

 off the south and south-west of the island. Here 

 again the phenomena are clear and comprehensible, 

 because they are, as it were, "writ large" — the 

 difference in temperature between the cold water off 

 the north and east and the warmer Atlantic waters 

 off the south and west of the island being very 

 marked, which renders the migration practically an 

 absolute necessity for the survival of the offspring. 

 Essentially the same in principle are the problems of 

 correlated physics and biology in British seas which 

 still, to a great extent, await elucidation. But here 

 the phenomena are not "writ large"; on the other 

 hand, they can only be demonstrated by the study of 

 observations made with fine precision and extended 

 over a considerable period of time. A. E. H. 



THE PARIS FLOODS. 



IT is now an evident fact that Paris has recently 

 suffered the ravages of an inundation greater and 

 more severe than any which have visited the city 

 within the last two and a half centuries. A gauge 

 at the bridge of La Tournelle shows the surface of 

 the water as having reached a height above the bed 

 of the river of 27 feet 10^ inches. Normally, it is 

 only about 8 or 9 feet, and it is necessary to go back 

 so far as the year 1658 in order to find any record 

 exceeding, or even approaching, this figure. At that 

 date the height attained was 28 feet loj inches. A 

 few years previously (1651) there was a flood of 25 feet 

 8 inches, and in 1649 another of 25 feet 2 inches. The 

 flood of i8o2, great as it was, did not exceed 24 feet 

 5 inches, and that of 1876 only reached 21 feet 11 

 inches. 



The known records are as follows : — 



February 1649 



Janmry 1651 



February 1658 



Ft-bruary 1690 



March 1711 



December 1740 



February 1764 



January 1802 



March 1X07 



January 1910 



NO. 2102, VOL. 82] 



ft. !n. 

 25 li 



25 S 



28 lOi 



24 9 



25 o 

 25 II 

 24 04 

 24 5 

 22 o 

 27 10^ 



The causes of the flood are not quite so obvious as 

 the effects. At first sight it would appear that there 

 is no very satisfactory explanation to be vouchsafed. 

 In the watershed of the Seine and its tributaries there 

 is an absence of lofty ranges with snow-capped sum- 

 mits, capable of producing copious liquidations such 

 as prevail in mountainous regions. But on the other 

 hand, there are numerous impermeable districts within 

 the Seine Basin where the rainfall finds its way almost 

 entirely into the river bed, and if to the effect of a 

 prolonged precipitation in these areas there be added 

 the far from negligible contribution of melted snow 

 from the impermeable iMorvan Plateaux, produced 

 under the influence of a sudden and abnormal rise in 

 temperature, we need not pursue inquiries very, much 

 further in order to arrive at an adequate solution of 

 the problem. 



The Seine at Paris is formed by the confluence of 

 three important streams : the Yonne, the Upper Seine, 

 and the Marne. Of these the Yonne is the only one 

 presenting torrential characteristics ; it rises rapidly, 

 and subsides as quickly. The other two streams move 

 more slowly, and change less abruptly. After a period 

 of heavy rainfall the flood waters of the Yonne arrive 

 first at the point of confluence, reaching it at the end 

 of three or four days, and they produce the greater 

 portion of the rise in level. Four or five days later 

 the waters of the Upper Seine and Marne arrive, 

 having been fed by filtrations through more permeable 

 ground and by surfeited springs, and these simply 

 serve to maintain the effect of the previous increment. 

 If towards the end of this period the previous meteoro- 

 logical phenomena in the upper reaches repeat them- 

 selves, the effect produced is that of a single con- 

 tinuous flood of considerable intensity. 



Fortunately, floods in the neighbourhood of Paris 

 can be predicted sufficiently in advance to enable 

 remedial, or at any rate palliative, measures to be 

 undertaken. The Seine, as has been pointed out, rises 

 but slowly, and the effects of floods in its affluents 

 are visible several days beforehand, and can be an- 

 nounced accordingly. There is ample warning for the 

 inhabitants to withdraw, if need be, from the threat- 

 ened quarters. An empirical rule has even been 

 established which enables the height attainable by 

 the flood to be approximately stated. The rise of 

 the Seine at Paris is just about double the mean of 

 the partial rises in its affluents at certain fixed points. 

 The hygrometric service of Paris, therefore, plays a 

 very useful part in issuing these forecasts, and renders 

 valuable service to the community at large. 



PROF. F. PURSER. 



THE news of the death of Prof. F. Purser, pro- 

 fessor of natural philosophy in the University 

 of Dublin, announced in last week's Nature, has been 

 received with deep regret. His life had just reached 

 the regular period of seventy years, and intellectually 

 he was as vigorous as ever. 



Prof. Purser was one of the ablest and most brilliant 

 members of a verv clever family. His father managed 

 Guinness's Brewery in the time of Sir Benjamin 

 Guinness, and it was to a great extent owing to his 

 skill, foresight, and enterprise that the brewery 

 attained the colossal dimensions it possesses at pre- 

 sent. His elder brother was a mathematician of a 

 very high class, and was for several years professor 

 in Queen's College, Belfast. 



Two of his cousins were distinguished professors 

 of the University of Dublin. One held the chair of- 

 institutes of medicine, or physiology ;_ the other. Dr. 

 Louis Purser, was professor of Latin, and is still 

 public orator. 



