December 20, 1900] 



NA TURE 



T95 



if the instrument would be trastworthy at the freezing-point of 

 mercury. Dr. Glazebrook asked how far the instrument was 

 suitable for Antarctic expedition work. He drew attention to 

 the difficulty of calibrating a new fibre should one get broken in 

 the field. Mr. Appleyard suggested the use of a bath kept at 

 constant temperature with a thermostat. Prof. S. P. Thomp- 

 son suggested a special meeting to discuss the physics of the 

 Antarctic expedition. Prof Threlfall said that there was no 

 difficulty in measuring the relation between temperature and 

 coefficient of stiffness down to very low temperatures. A more 

 difficult matter is the coefficient of temperature of the instru- 

 ment. Shrinkage of the instrument as a whole affects both the 

 fibre and the spring which supports it. The difficulty of a 

 broken fibre in the field can be got over by taking two or three 

 instruments. Working with a thermostat is useful in a labora- 

 tory, but decreases the portability in exploration work. — Mr. 

 Watson then exhibited a set of half-seconds pendulums. In 

 these pendulums special attention is paid to the stability of the 

 support. The pendulums are covered by a hood, from which 

 the air can be exhausted so that the logarithmic decrement is 

 diminished. The motion of the pendulums is shown by rays 

 of light reflected from right-angled prisms attached to them, 

 and the period of oscillation is determined by the method of 

 coincidences. For this purpose an accurate astronomical clock 

 is used, and observations are made continuously between 

 two time signals. An accuracy of one part in a million is 

 attainable. In reply to Prof Threlfall, Mr. Watson said that 

 the knife-edges were on the pendulums, and not on the sup- 

 ports. — The Society then adjourned until January 25, 1901. 



Cambridge. 



Philosophical Society, October 29. — The President, 

 Prof. A. Macalister, in the chair. — On the structure and classifi- 

 cation of the cheilostomatous polyzoa, by Dr. Harmer. This com- 

 munication dealt principally with the "compensation -sac, ";a name 

 given by Jullien to a delicate vesicle lying beneath the front wall 

 of the zooecia of many cheilostomes which have a rigid, calcareous 

 body- wall. This cavity, described by Busk in 1884, and with 

 more accuracy by Jullien four years later, has been looked for in 

 vain or altogether ignored by the majority of recent observers. 

 The compensation-sac is in reality an important organ in lepra- 

 lioid polyzoa, and Jullien's account of its relations is confirmed. — 

 Observations on the minute structure of the surface ice of glaciers, 

 by Mr. Skinner. By pouring plaster of Paris on the ice surface a 

 permanent cast can be obtained, from which it appears that the 

 porosity of the white superficial layer of a glacier arises from two 

 different causes. The first cause is the melting at the interfaces 

 of the crystalline granules, and the second lies in the formation 

 of small pits by the heat absorfjed and radiated from small 

 particles of dust. The two classes of holes are very distinct. 

 Those of the first kind are straight furrows joined to form rough 

 hexagons, and those of the second have a cylindrical or ellip- 

 soidal shape. These pits may occur anywhere on the exposed 

 surface of the crystal, and are like in shape to the larger pits 

 formed by small stones and gravel on the glacier surface. Some 

 other casts have been taken of the surface of the ice formed in 

 ice caverns (glacieres naturelles) ; these show only the melting at 

 the interfaces and no pits. In the glacieres the melting takes 

 place very slowly and is due almost solely to the contact of air 

 only slightly warmer than the melting-point. 



November 12. — Prof. Macalister in the chair. — (i) The 

 natives of the Maldives ; (2) The atoll of Minikoi, by Mr. J. 

 Stanley Gardiner. The Singhalese and Maldivians appear to be 

 the result of dichotomous branching of a common stem, one 

 division proceeding through the Laccadives to the Maldives, 

 the other travelling to its present home along the west coast of 

 Hindustan. Mr. J. Stanley Gardiner's second paper was taken 

 as read. The atoll of Minikoi is situated on a bank extending 

 down from the west coast of India to the south of the Maldives. 

 The atoll has in the past evidently been raised to a height of at 

 least twenty feet above the sea, before which it consisted of a 

 mere ring-shaped reef awash. The land is now very rapidly 

 being eroded on every side. The lagoon is broadening and 

 deepening, and the reef is markedly growing outwards. The 

 atoll probably grew up as a flat reef on some mound on the sea 

 floor, subsequently attaining its present shape. The numerous 

 deep bands of the Laccadives represent incipient stages in the 

 formation of reefs on such mounds, while the islands and reefs 

 exemplify the changes, which finally produce the perfect atoll. 



NO. 1625, VOL. 63] 



November 26. — The President, Prof. Macalister, in the chair. 

 — Some experiments on the electrical properties of a mixture of 

 hydrogen and chlorine, when exposed to light, by Prof. J. J. 

 Thomson. A series of experiments were made to see whether 

 there is any production of free ions when a mixture of hydrogen 

 and chlorine is exposed to light. If any such production took 

 place it would cause the electric conductivity of the mixed gases 

 to increase when exposed to light. This was tested by placing 

 a small gold-leaf electroscope inside the mixed gas ; the rate of 

 escape of electricity was found not to be affected by exposure to 

 light, either in the stage just after the incidence of the light 

 when the mixture expands, or in the subsequent stages when 

 the hydrogen and chlorine are combining. The problem was 

 then attacked from a different side and free ions produced in 

 the mixture by the aid of Rontgen rays or the radiation from 

 thorium ; though large numbers of ions were produced they 

 had no appreciable effect on the rate of combination of the 

 gases.— On the leakage of electricity through dust-free air, by 

 Mr. C. T. R. Wilson. — Elster and Geitel have shown that an 

 ' electrified body gradually loses its charge when freely exposed 

 in the open air or in a room. Their results are in agreement 

 with previous experiments of Linss. They conclude from their 

 experiments that free ions exist in the atmosphere. The 

 experiments described in this paper prove that ionisation can be 

 detected in a small closed vessel containing dust-free air not 

 exposed to any known ionising agents. To eliminate any 

 uncertainty due to leakage through the insulating supports, the 

 system from which the leakage was measured was fixed by 

 means of a small bead of sulphur to a conducting rod passing 

 through the wall of the vessel and kept at a constant potential 

 equal to the initial potential of the leaking system. To reduce 

 the capacity of the latter to the smallest possible amount, the 

 whole system from which the leakage was measured was reduced 

 to a small brass strip with a narrow gold-leaf attached, the 

 deflections of which, read by means of a microscope, served to 

 measure the potential. With a capacity of 73 centim. there is 

 a nearly constant fall of potential in a vessel containing 163 c.c, 

 of air at atmospheric pressure, amounting to 3 volts per hour, 

 the initial voltage being 220. The rate of leak is the same in 

 filtered air whether the apparatus be filled and used in the 

 laboratory (where contamination with radio-active substances 

 might be formed) or in the country. The leakage takes place 

 in the dark at the same rate as in diffuse daylight. The rate of 

 leak is the same for positive as for negative charges. The 

 quantity lost per second is the same when the initial potential is 120 

 volts as when it is 210 volts. Such voltages produce the " satura- 

 tion " current and the rate of leak may therefore be used to 

 measure the ionisation. The rate of leak is to a first approxi- 

 mation proportional to the pressure ; at a pressure of 43 millims. 

 the leakage is about one-fourteenth of that at atmospheric 

 pressure. If we take the value found by Prof. J. J. Thomson 

 for the charge carried by each ion, 6*5 x lo""* E. u., we can take 

 the experiments as indicating that 20 ions of either sign are 

 produced per second in each c.c. of air at atmospheric pressure. 

 — On a solar calorimeter used in Egypt at the total solar eclipse 

 of 1882, by Mr. J. Y. Buchanan. By means of this instrument, 

 which consists of a modified form of a Liebig's condenser 

 mounted equatorially, the solar radiation collected is condensed 

 48-fold. Observations made with it show that, taking the 

 radius of the earth's orbit to be 212 times the 

 radius of the sun, the radiation of one sq. metre of the sun's 

 surface is spread over 45,000 sq. metres of the earth's surface, 

 whence the sun must radiate energy at the rate of at least 

 37,300 horse-power per sq. metre of its surface. — Some theorems 

 in regard to matrices, by Mr. T. J. I' A. Bromwich. — On the 

 rational space curve of the fourth order, by Mr. J. H. Grace,— 

 On Trifolium pratense, var. parviflorwn, by Mr. I. H. Burkill. 

 — The writer has been able to examine plants of this so-called 

 variety from Britain and various parts of the Continent, and to 

 show that it is an abnormality in which the carpels are slightly 

 foliaceous, the corolla crumpled, and with a few secondary 

 modifications in other organs. 



Manchester. 



Literary and Philosophical Society, December 11.^- 

 Prof. Osborne Reynolds, F.R.S., Vice-President, in the chair. — 

 On the thermodynamical properties of superheated steam and 

 the dryness of saturated steam, by J. H. Grindley. The paper 

 contained a review of experiments with steam made by various 

 observers. Some calculations were given which showed the 



