June 14, 1900] 



NATURE 



16] 



one of which was provided with two simple prisms, the other 

 having three compound prisms. The spectra being obtained, 

 the inclination of the spectral lines and the difference of wave- 

 length of the light coming from the two opposite equatorial 

 limbs of the planet is measured, and alter corrections being 

 applied for the inclination of the planet's equator to the line of 

 sight, the resulting displacement indicates the e((uatorial velocity. 

 As the light from the planet is reflected sunlight, the value 

 measured is, of course, double the actual velocity. 



The complete measures from fourteen plates taken with the 

 two-prism spectrograph, and from five obtained with the instru- 

 ment furnished with three compound prisms, are given. The 

 values adopted are the means of measurements of from six to 

 sixteen spectrum lines on each plate. 



The photographs were obtained on the evenings of March 25, 

 30; April 4, 6, 7, 8, 10, II, 20, 28; May 4, 5, 13, with ex- 

 posures varying from 7m. to 60m. The angular diameter of the 

 planet varied from 8 "•6 to ii"'0. With the 30-inch refractor, 

 of about 40 feet focal length, the linear diameter at the principal 

 focus was I "2 mm., and this was further reduced by the relative 

 f)ci of collimator and camera objectives to o"8 mm. on the 

 photographic plate. 



From the difficulty of the determination it is to be expected 

 that the several means should vary for the different plates ; but 

 the extreme values given still prove the short rotation period. 

 Taking the diameter of Venus to be 12,700 km., the values of 

 the equatorial velocity {v) are as follows, the corresponding time 

 of rotation (T) being placed under each : — 



7'= 07 o"5 0*462 o*45 0'3 km. per sec. 



T=i5-9 22*1 24-0 24-6 370 hours. 



The author expresses the hope that the astronomers having the 

 control of the large telescopes at the Potsdam, Lick and Yerkes 

 Observatories will repeat his observations for confirmation or 

 revision. 



New Variable in Auriga. — Dr. T. D. Anderson, of Edin- 

 burgh, announces in the Astronomische Nachrichten (Bd. 152 

 No. 3642), the detection of a new variable star in Auriga. It is 

 not charted in the B.D. , and has the following position : — 



Decl. = ^ 50°i4'J^'^55o) 

 The changes in brightness during April and May 1900 were 

 from 8*3 to 8 '8 magnitude. 



Photographic Observations of Satellite of Neptune. 

 — In the Astronomische Nachrichten (Bd. 152 No. 3642), M. S. 

 Kostinsky gives the particulars relating to a series of deter- 

 minations of the satellite of Neptune, obtained from measures of 

 photographs taken with a telescope of 13 inches aperture at 

 Pulkowa. Many of the difficulties encountered in the photo- 

 graphic delineation of two neighbouring objects of very different 

 brightness have been previously discussed by the author {Bull. 

 de PAcad. Imper. des Sc. St. P^tersbourg, vol. vii. November 

 I 1897). In the present case of Neptune the problem is rendered 

 I slightly less difficult by the feeble brightness of the planet and 

 I the slow movement of the satellite. 



j The photographs described were obtained during the period 

 i 1899 February 4-March 25. the plates having exposures varying 

 j from 20m. to 60m. A table giving the corresponding calculated 

 I and observed values shows the method to be very accurate. 



SOME NOTES ON THE LATE PROF. PIAZZI 

 SMYTHS WORK IN SPECTROSCOPY. 



1 AMENTING, as we must do, that time has stolen from us 

 a mighty Ajax in the field of science, a sturdy, patient Atlas 

 who through more than half of this fast waning century robustly 

 upheld on his strong shoulders the growing spires and archi- 

 traves of science's ever-increasing edifice, it is with keenest 

 sorrow that the writer of these notes turns over the ample pages, 

 rich to profusion in details and superb in colour, of the monu- 

 mental works of spectroscopy left to us by the late Prof. C. 

 Piazzi Smyth, with the nearly hopeless intention of endeavouring 

 to give a short account of some of his most conspicuously im- 

 portant contributions to that branch of science. The late Prof. 

 Smyth was, indeed, no dilettante in the intricate and difficult 

 but fertile and alluring byways of science to which his leisure 

 moments were devoted ; and he was far from conceitedly or 

 afiectedly pedantic in the grasp of science which he brought 

 to bear upon his philosophical investigations. Although these 



NO. 1598, VOL. 62] 



embraced a range oi astronomical and meteorological subjects 

 which would singly engage all the energies of most men, and 

 their whole lifetimes to study with success, yet his mastery of 

 the state of science in the questions which he set himself to solve 

 or to explore, was acquired with so much inventive skill, un- 

 sparing pains and ardour, as always to make the character of the 

 work which he accomplished in them permanent and thorough. 

 Well accustomed as he was from his youth, and trained from 

 boyhood,^ to delicate telescopic, angular and micrometrical 

 measurements by eye and hand, he further possessed a gift of 

 great artistic skill in committing to paper, canvas, and even to 

 frescoes, beautiful drawings, photographs and coloured paintings 

 of the scenes of travel which he witnessed, and of sights which 

 clouds, the heavens, or his laboratory experiments disclosed to 

 him. This accomplishment, well illustrated, long ago, by his 

 publication in the Edinburgh Philosophical Transactions (vol. 

 XX. pt. iii. ) of a scene of darkness on the coast of Norway, near 

 Bergen, during the Total Solar Eclipse of July 1851, contributed 

 again in colours from his original, carefully kept paintings of the 

 scene, together with a similar view of the Zodiacal Light as 

 seen at Palermo in April 1872, to a new illustrated work on 

 astronomy published by Messrs. Cassell and Co. in 1894, led him 

 to leave to others the study of the actinic spectrum-regions with 

 the aid of photography, and to restrict his spectrum -measure- 

 ments entirely to all that could be seen and measured by the 

 eye alone, of the solar spectrum, or of the characteristic features 

 of gaseous bright-line spectra, in the whole visible portion of 

 the spectrum only. 



In his keen perception of all the grand sublimities of law and 

 order by which Nature's works are everywhere controlled and 

 guided and sustained, and in the constant intentness of his mind 

 to seek out these nature's workings, and to promulgate lucidly 

 and clearly his own perceptions and interpretations of them, 

 Ki<chhoff's great discovery, in 1859, that the chemical constitu- 

 tion of the sun could be read in its light's prismatic spectrum, 

 constrained him like a spell, as it quickly did many other physi- 

 cists, to devote much of his leisure time and abilities to spectro- 

 chemical researches. New striking truths were taught in 1860-61 

 by Sir William Huggins' not less surprising discovery from 

 observations of their spectra, of the gaseous conditions of certain 

 nebulre, and by Sir David Brewster's and Dr. J. H. Gladstone's 

 majestically mapped separation from the really solar dark lines 

 in the sun's spectrum, of its low sun, or terrestrial atmospheric 

 lines, soon afterwards distinguished by Secchi, Angstrom 

 and the first detector of the "rain-band" near solar D, in 

 America, Dr. J. P. Cooke, and especially by Dr. Janssen's 

 observations among the high Alps of Switzerland and experi- 

 ments with a long steam-tube in Paris, in 1866-7, in^o " aqueous- 

 vapour" and "dry-air" telluric lines. Kirchhoff's and Hof- 

 mann's first chemical investigation of the solar spectrum was 

 rapidly extended in the years from 1859 to 1868, with tables of 

 metallic and other elementary line-spectra by Huggins and 

 Miller, Mascart, Pliicker, Ditscheiner, Van der Willigen, 

 Thalen, Lockyer and others, into a wonderfully novel panorama 

 field of spectrum-analysis, chiefly applicable at first to celestial 

 chemistry and physics, but in such skilled hands as those of 

 Bunsen, Crookes, Reich and Richter, and later of Lecoq de 

 Boisbaudran and other able chemists, to the discovery also of new 

 terrestrial elements. The appearance at Upsala, in 1868, of 

 Angstrom and Thalen's classically accurate and chemically 

 expounded "Normal Solar Spectrum" map, with its line-places 

 in a natural diffraction -spectrum order of wave-length progres- 

 sion reckoned in " tenth-metres," or (io)'''th parts of a metre as 

 scale-units of wave-length,'^ and the detection with spectro- 

 scopes in the total solar eclipse of the same year in India, of the 

 hydrogen-flame nature of the sun's red prominences, seen in 

 full sunshine there by Dr. Janssen and almost simultaneously 

 also by Sir J. N. Lockyer in England, afforded to the new 



1 Under Sir Thomis Maclear's care, in JB36, at the a^e of seventeen ; at 

 the famous Observatory at the Cap; of Good Hope, where, during the List 

 three years, the presence of oxygen was discovered by its line-spectrum in 

 certain southern stars by the indefatigable English amateur astronomer, 

 Mr. F. Maclean ; ar.d where both that discovery and another by Sir J. N. 

 Lockyer of the presence of siliciuni in the same stars, have been confirmed, 

 and made independently by its energetic Director, Sir David Gill, with a 

 noble spectrophotographic 24-inch refracting telescope presented to the 

 Observatory under his own directions and liberal care for its completeness 

 by the same munificent explorer of stellar spectra in the northern and the 

 southern heavens, Mr. Frank Maclean. 



- It has now become a common usage in spectroscopy, microscopy and 

 molecular physics, to reckon such .small quantities as light wave-lengths in a 

 tenfold larger unit than the Angstrom one, denoting it by " mm," the 

 thousandth part of 'V," the thousandth part of a millimetre, " mm." 



