May io, 1906] 



NA TV RE 



41 



for the purpose; the melting point of gold (1064° C.) was 

 taki-n as the standard of reference. Pure palladium was 

 found to melt at 1541° C. and pure platinum at 1745° C. 

 Dr. Marker's recent determination of the melting point of 

 plalinum gave a value of 1710° C. 



In spite of its importance as a fundamental physical 

 constant, the latent heat of fusion of ice is known only 

 very approximately. The value obtained by Bunsen was 

 8003 cal., whilst Rcgnault found it to be 79-25 cal. In 

 the Journal dc Physique (vol. v., p. 157) M. A. Leduc 

 points out that Bunsen's result is subject to an error due 

 ito an incorrect determination of the density of ice at 0°. 

 .•\ re-determination of this constant gave a value of 0-9176, 

 and a re-calculation of the latent heat of fusion from 

 Bunsen's data, using this value, gave a result of 79-2 cal. 

 This is in close agreement with Regnault's determination. 

 The principal difficulty experienced in determining the 

 density of ice is in eliminating gas bubbles completely. 

 M. A. Leduc describes an arrangement by which he was 

 ■"nabled to minimise this source of error. 



Some remarkable specimens of phosphorescent calcite 

 from Joplin, Missouri, are described by Mr. W. P. Headden 

 In the .'\pril number of the American Journal of Science. 

 Some of the crystals, after being exposed to .sunlight, were 

 found to become highly phosphorescent, and to retain this 

 property for a period of thirteen hours. The specimens of 

 calcite which showed prolonged phosphorescence were 

 always yellow in colour, and contained 0007 per cent, of 

 •ceria, 0-012 per cent, of the didymium earths, and 0-013 per 

 <;ent. of yttrium and erbium ; the spectrum of the latter 

 was very distinct. Purple-coloured specimens of calcite 

 found in the same neighbourhood were shown to owe their 

 colour to the presence of didymium, and to differ from the 

 vellow calcite in being non-phosphorescent. So far as the 

 analytical evidence goes, the phosphorescence of the yellow 

 calcite seems to be associated with the presence of earths 

 of the yttrium group. 



A NUMBER of foliaceous and fruticose lichens collected 

 by Mr. A. W. C. Herre on the Santa Cruz peninsula, in 

 proximity to San Francisco, arc described by him in vol. 

 vii. of the Proceedings of the Washington .-\cademy of 

 Sciences. Parmelia is an important genus, as the species 

 are both numerous and conspicuous; Parmelia entcro- 

 nwrpha is a characteristic lichen of the red-wood forest, 

 and Parmelia Herrei provides a new species. The new 

 ■species Gyrophora diabolica forms in its locality, the 

 Devil's Cafion, the dominant feature of the lichen rock- 

 flora; another interesting species is the lace lichen, Ramalina 

 reticulata, that festoons the oaks. The writer has drawn 

 tip a useful key for the determination of genera, and keys 

 to the species. 



A ruBLiCATiON just received from the Harvard College 

 Observatory describes in detail, and with examples, a 

 telegraphic cipher code devised by Mr. W. P. Gerrish, of 

 that observatory. Numerous advantages are claimed for 

 this system over other systems now in use, its chief 

 characteristic being the ready transmission of groups of 

 figures in a form at once simple to dispatch and readily 

 translatable. A test of the system between the Harvard 

 and Lick observatories gave great satisfaction. 



Messrs. ■\rchib.-\ld Const.-\ble .-vnd Co., Ltd., will 

 -publish shortly a new book by Prof. H. C. Jones, of the 

 Johns Hopkins University, entitled " The Electrical Theory 

 of Matter and Radio-activity." 



Messrs. DAWB.iiRN .ind Ward, Ltd., are preparing a 

 new issue of their " Directory of Photographic Dark 



Rooms," and will be glad to receive from photographers 

 information as to any public dark room not included in 

 their directory. 



Some of the natural attractions of Norway are described 

 in an illustrated booklet just received from the Albion 

 Steamship Co., Ltd., Newcastle-on-Tyne, containing the 

 itinerary of fortnightly pleasure cruises to the Norwegian 

 fiords by the steam yacht Midnight Sun. The cruises are 

 arranged so that passengers may see the most interesting 

 scenery on or near the fiords from the Ryfylke to the 

 Romsdal, and ample time is allowed for excursions away 

 from the ship. 



.Mr. C. L. Muller has published a pamphlet giving an 

 illustrated description of Dr. Looser's double thermoscope 

 and some of the experiments possible with it. The instru- 

 ment is an mgenious form of differential thermometer in 

 which great sensitiveness is secured, and so arranged that 

 it is possible to use it in making quantitative determin- 

 ations. The booklet contains instructions for the perform- 

 ance of fifty-seven experiments in which the thermoscope 

 can be employed. 



OUR ASTRONOMICAL COLUMN. 



The Expected Return of Holmes's Comet. — From the 

 observations of Holmes's comet in 1S99-1900, Dr. H. J. 

 Zwiers has computed a set of elements of the comet's 

 path and an ephemeris for the probable reappearance of 

 the object during the present year. 



Having computed the elements for the epoch 1899, Dr. 

 Zwiers applied the Jupiter perturbations for the period 

 January, 1899, to April, 1906, and for January 16-0 

 (G.M.T.), 1906, found the following elements : — 



M = 35i 46 52'i4 



T =346 2 31 63 I 



a =331 45 407s -i9o6'o 



i = 20 48 53 -30 J 



(() = 24 20 25-55 

 /i= 5 1 7" 447665 

 log a = o-5574268 



NO. 1906, VOL. 74] 



The ephemeris computed from these elements extends 

 from May i to December 31, 1906, and is given, for every 

 alternate day, in No. 4085 of the Astronomische 

 Nachrichten. 



."According to the above elements, the perihelion passage 

 should have taken place at March 14-1804 (G.M.T.), 1906, 

 but, in a supplementary table. Dr. Zwiers gives the 

 ephemeris corrections which will become necessary should 

 it occur either four days earlier or later. 



The Luminosity of the Brighter Stars. — An interest- 

 ing discussion of the luminosity of the brighter .stars is 

 published by Mr. George C. Comstock in No. 3, vol. xxiii., 

 of the Astrophysical Journal. 



Of twenty-five stars discussed, the brightest in the 

 heavens, Mr. Comstock finds that twenty-two have 

 luminosities less than 1000, whilst three, j3 Crucis, Rigel, 

 and Canopus, have luminosities greatly exceeding this 

 value, the luminosity of the sun being taken as unity. 



In Mr. Comstock's opinion, this irregular distribution 

 of values and the enormous excess of the three exceptions 

 above the mean value render it unlikely that the parallaxes 

 hitherto accepted for these three stars are entirely trust- 

 worthy, for it is on them that the values obtained for the 

 luminosities are based. 



Surveying the whole discussion, Mr. Comstock arrives 

 at the conclusion that there is no adequate evidence that 

 the maximum of stellar luminosity exceeds 1000, and, 

 further, he opines that the mean luminosity of first-magni- 

 tude stars is not less than 100. 



The V.-vriable Radial Velocity of c Aurice. — In No. 

 4084 of the Astronomische Nachrichten Dr. H. Ludendorff 

 discusses the variable radial velocity of the star 6 Aurigaa. 



The variability of this object was discovered by Fritsch 

 in 182 1, and its variable velocity by Vogel and Eberhard 

 in 1902. 



The present discussion is based on the measurements of 



