May 5, 1899.] 



SCIENCE. 



66S 



lowering of temperature indicated by the plat- 

 inum thermometer in such circumstances did 

 not exceed one degree. Hence the platinum 

 must have come to a limit. Two pure platinum 

 thermometers which Professor Dewar had tried 

 both behaved in this way. Next he experi- 

 mented with a resistance composed of an alloy 

 of rhodium and platinum, which gave a different 

 temperature altogether. According to it the boil- 

 ing point of hydrogen was minus 246° as against 

 minus 238° shown by the pure platinum arrange- 

 ment, and it, too, failed to indicate the expected 

 lowering under exhaustion. A thermo-junction 

 of iron and German silver was next tried with- 

 out satisfactory results, and another junction of 

 lead and iridiumplatinum proved equally inef- 

 fective. Thus he was brought to an air ther- 

 mometer and the use of hydrogen itself under 

 diminished pressure to determine its own boil- 

 ing point. In the instrument he had construc- 

 ted the gas had a tension of 273 mm. at the 

 temperature of melting ice, so that a difference 

 of one millimeter, corresponded to one degree 

 of temperature. The boiling point of hydrogen 

 was by this thermometer given as about minus 

 252°, but various corrections had to be made, 

 and in particular the possibility of the hydro- 

 gen being contaminated with a slight impurity of 

 air or oxygen allowed for, so that it was uncer- 

 tain what exactly was the true boiling point. 

 Assuming it to be minus 2.52°, or 21° on the 

 absolute scale, Professor Dewar went on to il- 

 lustrate the difficulties of nearer approach to 

 the absolute zero itself. By exhaustion the 

 experimenter could not practically get more 

 than 6° lower, and at that point he was 

 barred and blocked with no means of bridg- 

 ing over the remaining 15°. Even supposing 

 that a new substance was discovered as volatile 

 in comparison with hydrogen as hydrogen was 

 in comparison with nitrogen, that under ex- 

 haustion would only give a temperature 3i° 

 above the zero, and it would require a second 

 hypothetical substance as volatile compared 

 with the first as the first was compared with 

 hydrogen to enable the experimenter to come 

 near the extreme of temperature he is aiming at. 

 The report by Sir William Crookes, F.R.S., 

 and Professor Dewar, F. R. S., on the compo- 

 sition and quality of daily samples of the water 



supplied to London for the month ending Feb' 

 ruary 28, 1899, says : We have again ta 

 record an excess of rain. The rainfall at 

 Oxford during the past month was 1.92 in., 

 the average fall for the last 30 years is 1.76 in., 

 giving an excess of 0.16 in., and making the 

 excess for the first two months of the j'ear 0.85 

 in., or 21.6 per cent, on the average fall. It is 

 interesting to observe the effect of the rainfall 

 on the number of microbes in the unfiltered 

 Thames water. No rain fell on the 1st, 2d or 

 3d, and the average number of microbes in the 

 Thames at Hampton up to the 4th was 6,510' 

 per c.c; it then rained every day until the 

 15th, during which time the average number 

 of microbes, including the 16th, rose to 38,354 

 per c.c; after the 15th no more rain fell, and 

 the average number of microbes from then to 

 the end of the month fell to 14,914 per c.c. 

 This large increase in the number of microbes 

 in the river, due to rain, originates not merely 

 from the washing of the surface of the land, 

 but is also largely due to atmospheric microbes 

 brought down by the rain. As far as our ex- 

 periments go they are perfectly harmless. 

 During the month the London waters, chem- 

 ically and bacteriologically, have maintained 

 their high character as an efficiently filtered 

 river supply. 



Professor E. Ray Lankester has written 

 a letter to the London Times stating that 

 £3,240 have been subscribed toward a second 

 expedition of Mr. J. E. S. Moore to Lake 

 Tanganyika, and that in addition £500 have 

 been offered on condition that a further sum of 

 £500 be collected. This insures the sending of 

 the expedition regarding the scientific impor- 

 tance of which Professor Lankester writes : 

 Some ten years ago the discovery of a true 

 medusa — similar to some marine jelly-fish — in 

 the waters of Lake Tanganyika led naturalists 

 to entertain the notion that this vast and re- 

 mote inland sea might retain within its area 

 other evidences of a former connection with the 

 ocean. The medusa (which swarms in the lake 

 at certain seasons) was duly described by Mr. 

 R. T. Giinther in my laboratory at Oxford, and 

 named Limnocnida Tanganyikse. So great was 

 the interest felt in the suggestions to which its 

 presence gave rise that I obtained two small 



