402 



NA TURE 



[February 22, 1900 



preparation of the plates is now well advanced. The work will 

 be issued in parts as fast as the letterpress can be got ready. 



ViOLURiC acid has already been utilised in calorimetric in- 

 vestigations in support of the ionic hypothesis, and in the current 

 number of the Berichte another physical constant, the electrical 

 conductivity, of this acid now gives rise to some interesting 

 speculations by Prof. Abegg, as to the changes preceding ion 

 formation. Starting with the experimental work of Guinchard 

 on the conductivity, and applying the well-known van 't Hoff 

 formula, the heat of dissociation of violuric acid is determined 

 from the temperature coefficient of its dissociation constant, 

 the values being - 3970 calories between 0° and 25° C, and 

 -3470 between 25° and 35° C. This is about ten times the 

 usual order of magnitude for acetic acid and most of the other 

 weak acids, and hence leads to the very plausible assumption 

 that here, as in other cases, the greater part of the heat of dis- 

 sociation is absorbed in intramolecular reactions which precede 

 the formation of the ions. In support of this is adduced the high 

 value found for the heat of dissociation of hydrofluoric acid 

 {-3550), as compared with the values for the other halogen 

 acids. Here the molecules are known to be HjFg, giving 

 first HF molecules, and finally ions. Water behaves similarly. 



The anomalous value obtained for the atomic weight of 

 tellurium, when viewed from the standpoint of the Periodic 

 Law, has led to numerous experimental researches upon this 

 constant. The value found has usually been higher than 

 MendeleefTs generalisation requires, and some observers have 

 suggested that ordinary tellurium may contain two substances. 

 The February number of the American Chemical Journal con- 

 tains a contribution to this subject by Messrs. Norris, Fay and 

 Edgerley, in which, as a preliminary to atomic weight determin- 

 ations, the preparation of pure tellurium was attempted. By 

 making use of the properties of basic tellurium nitrate, a metal 

 was obtained free from silver, gold, bismuth, arsenic, antimony, 

 and selenium, a specially delicate method being devised for the 

 detection of traces of the last named. The double chloride of 

 tellurium and potassium was then selected for careful study, 

 being subjected to a series of fractional crystallisations, but no 

 want of homogeneity could be detected in this way. Further 

 attempts are being made upon the dioxide. 



The additions to the Zoological Society's Gardens during the 

 past week include a King Vulture {Gypagus papa) from the 

 Rio Puri'is, presented by Mr. H. A. De Lisle ; a Weka Rail 

 {Ocydromus auslralis) horn. New Zealand, a Common Snake 

 {Tropidonotus wa/r/jf, albino), British, deposited; two Purple- 

 capped Lories (Lorius dromkella) from the Moluccas, 

 purchased. 



OUR ASTRONOMICAL COLUMN. 



Comet Giacobini (1900 a).— This comet has been observed 

 several times since its discovery at the Nice Observatory, but its 

 faintness will only permit of its observation with the largest 

 instruments. M. Javelle estimates it to be of the 13th magni- 

 tude. A telegram received from Kiel on February 19 gives the 

 following position : — 



R.A. 2h. 22m. 3s. \ 1900 February I7d. 8h. 2-5m. 



Decl. - 1° 19' 27"/ Nice Mean Time. 



The comet has continued its north-westerly movement from 

 Eridanus, the above position being nearly between the stars 

 S and Ceti (Mira). 



New Minor Planet C1899 E.Y.).— Recent observations of 

 this planet have enabled Herr Otto Knopf, of Jena, to revise 

 his elements and ephemeris, and he gives the new computations 

 in the Astronoviische Nachrichten, Bd. 151, No. 3621. 



NO. 1582, VOL. 61] 



Elements for 1^00 January q-q, Berlin Mean Time. 



Feb. 

 Mar. 



Harvard College Observatory. — In presenting the 

 fifty-fourth annual report of the Harvard College Observatory, 

 Prof. E. C. Pickering, the director, supplies evidence of an 

 unusually large output of work during the past year. With the 

 photometer mounted on' the east equatorial, over twenty-nine 

 thousand measures have been made by Prof. O. C. Wendell, 

 inchiding the photometric measurement of Jupiter's satellites 

 while undergoing eclipse, of the planet Eros, and of variable 

 stars of long period. The west equatorial has been employed 

 for visual examination of variables and comparison stars. Good 

 progress has been made with the reduction of the transit observa- 

 tions made by the late Prof Rogers in the years 1879- 1883. 



The new 12-inch horizontal meridian photometer has been 

 used in place of the old 4-inch instrument, which is now in Peru. 

 The director has made with this instrument 65,200 photometric 

 settings on 120 nights, and alter the year's trial the instrument 

 has proved extremely satisfactory in practice, it being found 

 that stars as faint as the 13th magnitude can bf measured at the 

 rate of one a minute, with an error of only about one-tenth of a 

 magnitude. 



Under the Henry Draper Memorial, 744 photographs have 

 been obtained with the 11 -inch Draper telescope, and 2395 

 with the 8-inch. The examination of the spectra on these plates 

 has led to the discovery of 23 new variables, 15 of which showed 

 bright line spectra. 



At Arequipa, in Peru, 686 photographs have been obtained 

 with the 13-inch Boydon telescope, and 693 with the 24-inch 

 Bruce doublet. It is hoped that the plates of Saturn taken in 

 August 1899 will furnish more accurate data for the orbit of the 

 recently discovered ninth satellite. 



At the Blue Hill Observatory the work has been practically 

 confined to obtaining automatic meteorological records of the 

 upper atmosphere by means of kites. The average height 

 reached by the meteorograph was 9650 feet from the ground. 



Prof. Pickering makes special mention of the serious conse- 

 quences to the work of the Observatory which may ensue, owing 

 to the continued fall of interest on the invested capital of the 

 institution. 



Interference Method of Measuring Small Dia- 

 meters.— The Bulletin of the French Physical Society, No. 

 143, contains an account, by M. Maurice Hamy, of the appli- 

 cation of interference. bands to the measurement of diameters 

 of small celestial bodies. The method, originally suggested by 

 Fizeau in 1868, was put to the test by Stephan in 1873, and 

 has been used by Michelson in 1892, who determined the 

 diameters of Jupiter's satellites with a 12- inch equatorial by 

 this means. M. Hamy's improvement consists in substituting 

 broad slits, allowing more light to pass than the narrow open- 

 ings employed in previous experiments. For the solution of 

 this problem a suitable formula has been found. The calculated 

 diameters of Jupiter's four principal satellites agree remarkably 

 well with the numbers found by Michelson, and M. Hamy's 

 estimated apparent diameter of the plant Vesta, viz. 0'54", is 

 exactly the value found by Barnard by micrometric observations 

 with the Lick equatorial. 



