90 



NA TURE 



[May 



1905 



the chief argument against it being that the ambiguity 

 of real and false effects only exists at the limit of vision, 

 whereas most of the canals considered are, isihen well seen, 

 far within this limit. . 



A number of interesting points concerning the canal 

 systems are deduced from the iqo3 observations, but only 

 one or two of the more striking may be mentioned here, 

 (i) The majority of the double canals do not exceed 3 -2 

 (degrees on the planet's surface) in width ; (2) at the time 

 of maximum visibilitv the two members of each double 

 are generally of equal strength, but as they wane one of 

 them usually becomes apparently stronger than the other; 

 (3) the double canals appear to congregate in special longi- 

 tudes and latitudes, in the latter case especially favouring 

 the equatorial regions, a fact which Mr. Lowell urges as 

 an argument against the " diplopic " theory ; (4) the double 

 canals are peculiar to the lighter regions of the planet s 

 surface, although single canals are, apparently, just as 

 numerous in the darker as in the lighter regions ; the 

 double canals, however, are always connected, directly, or 

 through the medium of similar objects, with the darker 

 areas. " 



Catalogue of New Double Stars. — Prof. Hussey's 

 ninth catalogue of double stars, discovered with the 12-inch 

 and 36-inch refractors of the Lick Observatory, and mostly 

 measured with the latter instrument, is contained in 

 Bulletin No. 74 of that observatory. The preceding cata- 

 logues have severally appeared in Nos. 480, 485, and 494 

 of the Astronomical Journal, and Nos. 12, 21, 27, 57, and 

 65 of the Lick Observatory Bulletins. 



The present publication 'gives the catalogue and D.M. 

 numbers, the position and the distance and position-angle 

 determined at each observation for each of the double 

 stars recorded. The catalogue numbers extend from 801 

 to 1000 inclusive, and run consecutively. 



M' 



THE ROYAL SOCIETY CONVERSAZIONE. 



' ANY instruments and devices of scientific interest were 

 shown at the Royal Society's conversazione on 

 Wednesday, May 17. As usual, the exhibits illustrated 

 methods and results of recent work in various branches of 

 science, and the subjoined summary of the official cata- 

 logue contains a few particulars relating to them. 



In the course of the evening lantern demonstrations were 

 given in the mecling-room by Dr. E. A. Wilson, Sir Oliver 

 Lodge, and Mr. Perceval I^andon. Sir Oliver Lodge 

 demonstrated the use of electric valves for the production 

 of high-tension continuous current. Electric vacuum 

 valves, which it is now found were suggested in a letter 

 by Sir George Stokes twenty years ago, have as their 

 function the entrapping of a portion of electricity by per- 

 mitting its passage in one direction and stopping its 

 return. They therefore can be employed to accumulate 

 electricity supplied from an intermittent or jerl<y source and 

 to store it at a steady high potential ; so that it may there- 

 after maintain a current through a very high resistance, 

 as in electrostatics, and may produce X-rays, or point- 

 discharge, or other continuous high-tension effects, and 

 enable a small portable coil to imitate some of the 

 effects of a much larger one by storage and accumulation 

 of impulses. Among the applications contemplated are the 

 separation of metallic fume and the dissipation of fog. — 

 Dr. Edward A. Wilson showed a number of Antarctic 

 views illustrating the life and work done on board the 

 Discovery during the years 1902 to 1904, and views of the 

 seals, penguins, and other birds met with in the Antarctic 

 circle ; and Mr. Perceval Landon exhibited pictures of the 

 road to Lhasa. 



The other exhibits are here grouped together according 

 to subjects more or less closely related to one another. 



Specimens illustrating the action of light and of radium 

 upon glass : Sir William Crookes, F.R.S. (1) It is well 

 known that many samples of colourless glass containing 

 manganese slowly assume a violet tint when exposed to 

 sunlight. In some specimens of glass exhibited the pieces 

 were of all depths of tint, from deep violet, almost black 

 in thick pieces, to pale amethyst. Analysis shows the 

 glass to contain manganese. Heating the glass in a 

 covered crucible to its softening point discharges the colour, 



NO. 18 6, VOL. 72] 



leaving the glass white and transparent. The coloration 

 is not superficial. On immersing a piece of the coloured 

 glass in a liquid of about the same refractive index as 

 itself, the colour is seen to have penetrated throughout 

 the mass. Radium, acting for a few days, even through 

 quartz, will produce as intense a coloration in a piece of 

 this glass as exposure to the sun on the Pampa has taken 

 years to effect. Six pieces of glass from the greenhouses 

 at Kew Gardens illustrated changes which took probably 

 about fifty years to complete in our climate. Purple spots 

 were produced on two of these specimens by Sir William 

 Crookes by the action of 15 milligrams of radium bromide 

 in a quartz tube in the course of ten days, the beginning 

 of change being well marked at the end of two days. In 

 a specimen of manganese glass exposed to light for forty 

 years as a pane of a greenhouse, the ends of the glass 

 which had been protected from light by the window frame 

 were colourless. In the expectation that radium might 

 have a reducing effect on the manganese compound, Mr. 

 F. Soddy submitted a porlion of the pane to the action 

 of 30 milligrams of radium bromide for three days _ in 

 May, 1904. The colour, however, instead of being 

 diminished, was intensified. Specimens were also shown 

 illustrating the coloration of glass, quartz, and fluorspar 

 by the rays of radium. 



Action of actinium or emanium emanation on a sensitive 

 screen : Sir William Ramsay, K.C.B., F.R.S. Actinium 

 or emanium are different names, adopted by Debierne 

 and Giesel respectively, for the same substance, separable 

 from pitchblende, and accompanying lanthanum. It gives 

 off an emanation, of which the period of activity is very 

 short— a few seconds. When this emanation impinges 

 on a sensitive zinc sulphide screen, the screen becomes 

 luminous. The luminous patch can be blown away, and 

 in a second or two reappears. — Phosphorescence caused by 

 the e rays of radium : Mr. G. T. Beilby. Phosphorescence 

 of calcspar and other substances— (i) during exposure to 

 the rays ; (2) after removal from the rays ; and (3) revived 

 by heat after secondary phosphorescence has died down. 

 The storage of phosphorescence and the coloration effects 

 are due to partial electrolysis of the calcium carbonate or 

 other substance by the stream of negative electrons.^ A 

 proportion of the ions re-combine at once, others continue 

 to re-combine after the rays have ceased to act, and the 

 remainder only re-combine when the mobility of the crystal 

 molecules is increased by heat. — Skiagrams of the hands 

 of Machnow, the Russian giant, and of O'Brien, the Irish 

 giant : Mr. S. G. Shattock. 



Large echelon spectroscope : Prof. A. Schuster, F.R.S. 

 This echelon spectroscope, constructed by Messrs. Adam 

 Hilger, Ltd., consists of 33 plates, and has a resolving 

 power equal to that of an ordinary grating of 329,000 

 lines in the first order. — A hand refractometer : Mr. G. F. 

 Herbert Smith. By means of this form of refractometer 

 the refractive indices of any translucent substance, the 

 refractive power of which lies within the effective range of 

 the instrument, 1400 to 1-760 approximately, may be 

 determined with ease and celerity, to units in the second 

 place of decimals if ordinary light, and to two or three 

 units in the third place of decimals if the monochromatic 

 light emitted by a volatilising sodium salt be the source 

 of illumination. — The Ashe-Finlayson comparascope : Mr. 

 D. Finlayson. This accessory to the microscope has been 

 designed to enable the images of two different objects, 

 separately mounted, to be projected side by side into the 

 field of view, thereby enabling a thorough comparison to 

 be made of their respective points of difference and re- 

 semblance. The apparatus consists of a prism placed 

 above the primary objective which reflects to the ocular 

 the rays from a secondary objective placed at right angles 

 to the optic axis of the microscope. — (i) Torsion balance, 

 used in radiation pressure measurements, by Nichols and 

 Hull ; (2) vacuum tube, of Nichols and Hull, to illustrate 

 the repulsion of comet tails by the sun : Prof. E. F. 

 Nichols. — .'Vn optical appliance to facilitate visual percep- 

 tion of ultra-microscopic particles : Mr. Carl Zeiss. The 

 apparatus consists of a projection table provided with an 

 arc lamp, optical bench, two projection aplanats, and a 

 precision slit. (The use of sunlight instead of the arc 

 lamp is preferable.) Particles of far less than half a 

 wave-length can be made visible with this apparatus. — 



