84 



NATURE 



[June 25. 1903 



optically flat" mifrors of such size and so great perfection 

 was a very great achievement." 



Radiant Points of July and August Meteors. — A paper 

 by Mr- Denning in No. 3874 of the Astronomische Nach- 

 richten describes the meteor showers which occur about 

 the same time of the year as the splendid Perseid shower, 

 and it gives, in tabular form, the radiant points of more 

 than one hundred showers that have been observed at 

 Bristol, during 1876-1902, in the months of July and 

 August, dividing the epochs of appearanceinto three periods, 

 viz. July 6-16, July 20-August 16, and August 19-25. 

 Many of the displays are feeble, and a prominent feature 

 of these is that they appear foir a long period from the same 

 fixed radiant. , " 



;]_The Perseid swarm varies greatly in intensity ; at some 

 apparitions as many as 156 to 200 shooting stars are 

 observed per hour, whereas at other appearances the hourly 

 rate may decline to 20 or 30. From, a careful survey of the 

 records, Mr. Denning thinks that there is evidence of this 

 shower having a periodicity of betA^een 104 and. 123 years. 

 The maximum is now reached on the morning'of August 

 12 or 13. 



Sun-spots and Terrestrial Temperature. — In discussing 

 the statement recently made by M. C. Nordmann - in its 

 application to the temperatures observed at the Jacob camp 

 (Guadeloupe), M. Alfred Angot finds that approximately 

 the same law holds good, and may be represented by the 

 formula 



t = t^ + ar, 



where t is the actual temperature, r is Wolf's frequency 

 number, and t„ and a are constants for each station, a being 

 a negative quantity. On calculating the temperatures for 

 the Jacob, station from this formula, first determining the 

 constants for that place, it is found that they vary but 

 slip-htly from the observed values, the mean variation being 

 + o°-o6 C, and M. Angot suggests that an analysis of the 

 annual variations at a number of stations might reveal the 

 presence of further periodical variations {Comptes rendus, 

 No. 21). 



The Satellites of Saturn. — Bulletin No. 34 of the Lick 

 Observatory contains the results of a second series of 

 observations of the satellites of Saturn made by Mr. W. J. 

 Hussey of that observatory. 



Mr. Hussey measured the position angles and distances 

 of each satellite in respect to one of the others, and gives 

 a table containing all the details of each observation ; he 

 concludes from estimations of their respective light values 

 that Mimas is probably larger than Hyperion, and, from 

 hi;-, measurements, that the generally accepted diameter of 

 Titan is undoubtedly too large ; 2500 miles is, according to 

 him, a much nearer approximation to the true value than 

 the values given in most text-books. 



HE ROYAL SOCIETY CONVERSAZIONE. 



M 



ANY of the objects on view at the Royal Society con- 

 versazione on Friday last were shown at the gentle- 

 men's conversazione held on May 15, and have already been 

 described in these columns (p. 59)'. There was, however, 

 a number of additional exhibits illustrating methods and 

 results of recent work in many branches of science, and 

 these are mentioned below. 



The condensation of the radio-active emanations of radium 

 and thorium by liquid air formed the subject of an exhibit 

 by Prof. E. Rutherford, F.R.S., and Mr. F. Soddy. The 

 radio-active emanations of thorium and radium appear to 

 be the residues of the thorium atom and radium atom re- 

 spectively after the heavy positively charged particles, 

 known as the " o rays," have been projected. They have 

 all the properties of inert gases of the argon family, and 

 diffuse away from the radium and thorium compounds pro- 

 ducing them. They can be condensed at the temperature 

 trf liquid air, and are again volatilised on raising the tempera- 

 ture. Their actual quantity is almost infinitesimally small, 

 being quite invisible and unweighable, but their presence 

 can be detected by their property of radio-activity. 



NO. 1756, VOL. ^8] 



A method for the rapid determination of the specific' 

 gravity of blood, taken from a single drop, was shown by 

 Prof. W. J. Sollas, F.R.S. A fluid heavier than the blood 

 (chloroform and benzole sp. gr. 107), and another lighter 

 (benzole and chloroform sp. gr. 1-04), are introduced into 

 a tube, the heavier first, so that the lighter, added sub- 

 sequently, floats upon it. The two fluids mix by diffusion 

 so as to produce a column in which the specific gravity 

 varies continuously from a higher to a lower value up- 

 wards. A drop of blood obtained from a pin prick is then 

 added, and sinks in the column until it reaches a level 

 where the specific gravity is identical with its own. Two 

 glass floats of known specific gravity are now introduced, 

 one of higher and the other of lower specific gravity than 

 the blood. The distances of these, when floating in the 

 column, from the drop of blood are proportional to the 

 difference in specific gravity. 



Mr. J. Y. Buchanan, F.R.S., exhibited a copper sphere 

 and brass tube in illustration of an effect produced by the 

 momentary relief of great pressure. Experiments were' 

 made during the cruise of the Challenger and on board the 

 Princess Alice. The copper sphere contained a glass 

 spherical flask of about i| inches in diameter hermetically 

 sealed, and the sea water had free access through the two 

 holes at the poles. The brass tube contained a glass tube 

 of 50 cubic centimetres in capacity, hermetically sealed, and 

 the sea water had free access at both ends of the brass tube. 

 The brass tube was sent to a depth of 3000 metres, and at 

 some, probably less, depth the internal glass tube gave way 

 to the pressure and collapsed suddenly. The enclosing 

 brass tube was pinched up by the external pressure. The 

 experiment shows that, in the time, it was easier to pinch 

 the envelope of brass than to shove in the plugs of water 

 at both ends. The copper sphere was sent first to 300a 

 metres, but was pulled up without showing any effect. It 

 was then sent to 6000 metres, and the internal glass flask 

 collapsed at some depth between 3000 and 6000 metres, and 

 the creasing which is visible on the copper sphere was pro-* 

 duced. These experiments, whether made with the copper 

 ball or with the brass tube, furnish striking demonstrations 

 of the importance of the element of time in all physical 

 considerations. 



Photographs of the paths of aerial gliders were shown- 

 by Prof. G. H. Bryan, F.R.S. , and Mr. W. E. Williams. 

 These photographs weie taken by attaching a piece of 

 magnesium wire to gliders of cardboard, and show the path 

 taken during their descent through the air. By fixing a 

 rotating wheel in front of the camera so as to give a series 

 of exposures instead of a continuous exposure, dotted traces 

 were obtained, the distance between the dots enabling the 

 velocity at different points to be compared. 



The solar disc in monochromatic (k) light was exhibited 

 by the Solar Physics Observatory, South Kensington. The 

 glass positive and negative shown was a specimen of one 

 of the trial plates taken for adjustment of the new photo- 

 spectroheliograph. Large belts of prominences could be 

 seen stretching across the solar disc. 



The Solar Physics Observatory also exhibited photographs 

 of the spectrum of lightning. The spectra were secured by 

 Dr. William J. S. Lockyer on the early morning of May 31. 

 Small cameras were employed fitted with Thorpe's trans- 

 parent gratings in front of the lenses. 



A reproduction of the hydraulic organ of the ancients 

 was shown by Mr. John W. Warman. This instrument, 

 originally invented by Archimedes about 250 B.C., has 

 furnished a problem for at least 600 years, and has been 

 the subject of endless speculation. The only real difference 

 between the hydraulic and the ordinary or " pneumatic " 

 organ is that, in the former, the wind-pressure is derived 

 from the weight of an annular mass of water, instead of 

 from the loaded top of a folded air-bellows. 



Mr. W. N. Shaw, F.R.S., had on view the July number 

 of the Monthly Pilot Charts of the North Atlantic and 

 Mediterranean, issued by the Meteorological Council. The 

 chart was exhibited to show the modifications introduced 

 since the commencement of the series in April, 1901. 



Bactericidal emanations from radium were demonstrated 



by Mr. Henry Crookes, who also showed photographs of » 



; box of instruments, (a) taken by ordinary Rontgen rays, 



I (b) taken by radium emanations at a distance of eighteen 



: inches. 



