November 13, 1885.] 



SCIENCE. 



437 



Two of these Benoit standards gave different 

 results at different times. For instance, one whose 

 resistance had been designated as 1.00045 legal 

 ohms by Benoit, showed, when first filled, the 

 same resistance in terms of the Cambridge stand- 

 ai'ds ; the next day its resistance was found to be 

 1.00071, and, on flowing the mercury back and 

 forth through it, it rose to 1.00080. The tube was 

 examined, but no ti'ace of an air bubble was seen. 

 It was then cleaned and filled again, and afterwards 

 gave consistent results, the mean being .99990 legal 

 ohms, though the same precautions were taken 

 in the first filling as in the last. This result indi- 

 cates the uncertainty of mercury standards, and 

 the extreme care that is required to obtain con- 

 sistent results. Every mercury standard should 

 be made of such a form that the tube can not only 

 be washed, but wiped out by some mechanical 

 means. It is important to notice that the rate at 

 which the resistance of mercury varies with the 

 temperature has been examined lately by Mr. 

 Glazebrook, and he finds that the rate of change 

 diminishes rapidly as we approach 0°; the average 

 change between 0° and 5° being .000834, while 

 between 0° and 15° it is .000879. 



CHOLERA PROSPECTS FOR ENGLAND. 



In regard to the prospect of the cholera reach- 

 ing England this season, the Lancet of Oct. 24 

 says : We have now reached a period when we 

 may fairly form a judgment as to the more im- 

 mediate cholera prospects for England. Although 

 cholera in Europe usually follows certain definite 

 rules as to climate and season, yet it deviates from 

 these sufi&ciently often to impart an element of 

 uncertainty to any opinion concerning its move- 

 ments. But notwithstanding this, the chances of 

 any extension of the present epidemic to this coun- 

 try are now so remote that we may fairly conclude 

 that we have for a third year escaped from the 

 danger with which we have been threatened. It 

 is true that in 1884 our greatest danger did not 

 arrive until Paris had become infected, and that 

 this did not take place until we were well into the 

 first week of November ; but, on the other hand, 

 the extent and the area of diffusion of cholera in 

 France was last year far greater than it has been 

 this year, and cholera deaths occurred in 1884, 

 both at Toulon and Marseilles, until about the end 

 of November. This year, on the contrary, France 

 has x^ractically been free from cholera for some 

 time, and the main risk we have to contend with 

 lies in our shipfjing relations with Spain and Sicily, 

 and these are limited both in amount and in the 

 number of home ports concerned. So, also, we 

 have had evidence that the vigilance and activity 



which have been exercised by our port authorities 

 with regard to any such importations have been 

 successful, even when, in a few occasional in- 

 stances, there was reason to believe that isolated 

 cases of the disease had found their way to our 

 shores. And, further, the danger from places in 

 the south of Europe, which are still infected, is 

 every week becoming less by reason of a general 

 subsidence of the epidemic. On the whole, there- 

 fore, we may with a considerable degree of con- 

 fidence conclude that we have another season 

 before us during which we may, unhindered by 

 any element of panic, go on maturing our prep- 

 arations to withstand such danger of cholera 

 importation as may recur next year ; and we have 

 the satisfaction of knowing that the preparations 

 needed are precisely those which will tend to 

 diminish mortality from other causes than cholera, 

 and that the needed expenditure will in the end 

 tend to our prosperity. 



ARTIFICIAL PROPAGATION AND CULTI- 

 VATION OF OYSTERS IN FLOATS.' 



Without expressing any opinion as to the value 

 of the process of ' fattening ' oysters by placing 

 them for a few days in cars floating in fresh water, 

 I wish to point out that there is no similarity 

 between this process and the process of propaga- 

 tion which is here described. 



My attention was first called to the value of 

 floating cars in oyster culture by Mr. William 

 Armstrong of Hampton, Virginia, who informed 

 me in 1884 that 'seed' oysters, which he had 

 placed in floating cars in the mouth of Hampton 

 Creek, grew more rapidly, and were of a better 

 shape and more marketable, than those which 

 grew from seed planted on the bottom in the usual 

 way. 



One of the results of my study in 1879, of the 

 development of the oyster, was the discovery that 

 there is a period of several hours, immediately 

 after the embryo acquires its locomotor cilia, when 

 it swims at the surface, and this is the period when 

 it is swept into contact with collectors. As soon 

 as the shell appears, the larva is dragged down by 

 its weight, and either settles to the bottom and 

 dies, or swims for a time near the bottom. The 

 tendency to swim at the surface is an adaptation 

 for securing wide distribution by means of the 

 winds and currents which sweep the young oysters 

 against solid bodies which may serve for attach- 

 ment ; and the greatest danger to which the oyster 

 is exposed, at any part of its life, is that it may 

 not, at the swimming stage, find a clean, hard sur- 

 face for attachment. 



1 Prom Johns Hopkins university circulars, October. 



