208 



NA rURE 



[June 29, 1905 



TELESCOPIC WORK FOR OBSERVERS OF 



PLANETS. 

 'PHE possessors of telescopes now huve an interesting 

 -*■ variety of planetary objects for examination. These 

 are Venus, Mars, Jupiter, Saturn, and Uranus. 



Venus is visible, as a crescent, in the morning sky, 

 increasing to half-moon shape in the second week of July, 

 and arriving at her greatest elongation, west of the sun, 

 on July 6, when her distance from that luminary will be 

 45° 44'. The conjunction of \'cnus and Jupiter will form 

 an attractive spectacle on July 4. 



Mars has now declined in diameter to 13", but the 

 principal markings are still very distinct, and some of the 

 more delicate canals remain observable. -After July the 

 planet will have receded so far from the earth that further 

 telescopic study of his physical lineaments cannot be pur- 

 sued successfully. 



Jupiter has just emerged into view as a morning star, 

 rising about 2^ hours before the sun. The most interesting 

 point to be determined is the present position of the great 

 red spot. The motion of this remarkable object has been 

 curiously variable in recent years. Between October, 1904, 

 and March, 1905, the rotation period corresponded very 

 closely with that of system ii. of the ephemeris based 

 on gh. 55m. 40-635., and the longitude remained constant 

 at about 26°, so that the spot followed the passages of the 

 zero meridian by 43 minutes. The exact position of the 

 marking should be ascertained as early and as frequently 

 as possible during the coming opposition, and the follow- 

 ing are the probable times of a few transits during ensuing 



Approx 



weeks 



July I 

 6 



23 



13 49 



The large dark spot seen in the south temperate zone 

 of Jupiter in and since iqoi, if still visible, will be in 

 longitude 191° at the end of June, and will therefore 

 follow the zero meridian by 53 hours and the great red 

 spot by 4^ hours. 



Saturn rises 5 hours before the sun. It is most im- 

 portant to learn whether there are any lingering signs of 

 the extensive disturbance which affected the northern hemi- 

 sphere in the summer and autumn of 1903. It is singular 

 that, though a large number of observations of the spots 

 were made and promptly reported in 1903, we. have heard 

 practically nothing of similar results in 1904. Yet the 

 markings remained visible, if much less conspicuously, in 

 1904. 



Uranus was in opposition to the sun on June 23, and 

 is therefore easily discernible at the present time, though 

 his southern declination is 23^° .An excellent opportunity 

 will be afforded of identifying this planet during the third 

 week in July, when he passes about i minute of arc north 

 of the star i Sagittarii (mag. 53). 



Added June 25. — The great red spot on Jupiter was 

 seen by the writer at Bristol, and estimated central on 

 June 24 ijh. 43m. Its longitude was therefore 25°.i, and 

 this sufficiently shows that its motion has exhibited no 

 further change during the last three months. 



Saturn was also carefully examined on the same morn- 

 ing, but no conspicuous spots w-ere seen in a isi-inch 

 reflector by Calver, power 235. The observation of Jupiter 

 was obtained with a lo-inch reflector bv With-Browning, 

 power 205. W. F. Denning. 



THE ROYAL SOCIETY CONVERSAZIONE. 

 T^HE second, or ladies', conversazione of the Royal 

 Society was held in the rooms of the society at 

 Burlington House on Friday last, June 23, and was 

 attended by a large and distinguished company. As on 

 former occasions, many objects of scientific interest were 

 exhibited, but most of them were shown at the earlier 



NO. 186 1, VOL. 72] 



conversazione on May 17, and have already been described 

 in these columns (May 25, p. 90). It is therefore only 

 necessary now to refer to additional demonstrations and 

 exhibits. 



In the course of the evening there were demonstrations, 

 with lantern illustrations, on recent work in mimicry and 

 protective resemblance, by Prof. E. B. Poulton, F.R.S., 

 and on the three-colour photographic process, by Sir 

 W. de W. Abney, K.C.B., F.R.S. The photographs in 

 colour that were shown were prints from three negatives 

 taken of each subject. Each of the three negatives was 

 taken through an appropriate coloured medium, and the 

 three transparent prints were projected on a screen with 

 appropriate coloured screens behind them, giving the 

 colours of nature. The process and apparatus employed 

 were based on those of Mr. Ives. 



Brief descriptions of the new exhibits are given in the 

 subjoined abstract of the official catalogue. 



The metal sodium, prepared so as to show its true colour 

 and lustre : Mr. G. T. Beilby. The specimen w-as prepared 

 by Dr. Thomas Ewan by melting the metal in vacuo in one 

 vessel and running the clean, bright part of the liquid into 

 another communicating vessel which had been freed from 

 condensed air or moisture by heating during exhaustion. 

 .After solidification of a crystalline crust on the glass, the 

 surplus liquid was run back into the first vessel and the 

 specimen globe was sealed off. — (i) Pictures produced in 

 the dark on a photographic plate by different woods ; 

 (2) ordinary photographs of the same woods ; (3) the woods 

 used in the experiments : Dr. W. J. Russell, F.R.S. The 

 pictures taken in the dark were obtained on an ordinary 

 rapid photographic plate, the wood being in contact with 

 the plate from one to eighteen hours at a temperature of 

 £;£^° C. The pictures were developed in the same way as 

 if they had been produced by light. 



The entoptoscope, a new form of ophthalmoscope : Prof. 

 W, F. Barrett, F.R.S. The instrument was devised by 

 the exhibitor for the self-examination of the eye by means 

 of pinhole vision — entoptic diagnosis (Listing). When an 

 illuminated fine pinhole in a sheet of metal is held near the 

 eye, sharp shadows of any opaque or semi-opaque object in 

 the path of the rays within the eyeball are thrown on 

 the retina. By this means the growth of cataract from 

 its earliest stages can be traced. By using two closely 

 adjacent pinholes in the revolving diaphragm, and the 

 transparent scale in the eye-piece, the exact magnitude 

 and distance from the retina of the opacity can be deter- 

 mined. — The F.ttles-Curties ophthalmometer and ophthalmic 

 microscope : Mr. C. Baker. The opththalmometer is an 

 instrument for measuring the radius of cur\'ature of the 

 cornea, and consequentlv of ascertaining the dioptric value 

 of the refracting medium bounded by that curvature. The 

 instrument consists of an attachment by which the patient's 

 head is steadied, and a telescope with Wollaston prism 

 for observing the images of the " liiires." The latter are 

 carried on an arc graduated in terms of dioptres and radius 

 of curvature, and prismatic steel bars provide a steady 

 movement by rack and pinion to the adjustable parts. 

 The whole is mounted on a telescopic floor standard which 

 contains a plunger actuated bv a spiral spring ; by slight 

 pressure this can be pushed down to the level of the 

 patient's eye and clamped. The ophthalmometer can be 

 detached ,and a microscope provided with electric illumin- 

 ation substituted. 



Tantalum, and tantalum electric lamps : Messrs. Siemens 

 Bros, and Co., Ltd. The exhibit comprised (i) specimens 

 of the metal tantalum in the form of small blocks of more 

 or less purity, also sheets and metallic powder, and speci- 

 mens of wire of various thicknesses ; (2) a series of 

 tantalum glow lamps, requiring no volts and 034 ampere 

 to give a light of 25 \.C. (li watts per candle-power). — 

 The " Osmi " incandescent lamp : the General Electric 

 Company. The lamp in appearance is similar to the 

 ordinary electric bulb, but in place of carbon the filament 

 is made from the rare metal osmium, which, when in a 

 state of incandescence, glows with extreme brilliancy. The 

 advantages claimed are : — high fusing point, white light, 

 higher electrical efficiency, longer life, saving of current, 

 less heat. The blackening of bulbs is inappreciable. The 

 consumption of current with ordinarv carbon filament lamp 

 is 3.5 to 4 watts per candle-power. Consumption of current 



