March i6, 1Q05J 



NA TURE 



469 



sheets of metals. It is, however, shown by J. Precht and 

 C. Otsuki, in the Verhaitdlungen of the German Physical 

 Society (vol. vii. p. 53), that hydrogen peroxide itself is 

 capable of penetrating thin films of gelatin, celluloid, india- 

 rubber and black paper, the peroxide being subsequently 

 capable of detection by titanic acid. Metals in the form 

 of the thinnest sheet are, nevertheless, impervious to hydro- 

 gen peroxide, if small holes be not present ; the same is 

 true of thin films of paraffin, glass, and ebonite. 



Two papers dealing with the accurate measurement of 

 coefficients of expansion are contained in the January num- 

 ber of the Physical Review. Mr. H. McAllister Randall 

 describes the determination of the coefficient of expansion of 

 quartz between th,e temperatures of 36° and 500° C. by 

 means of Pulfrich's optical method, and shows that up to 

 about 250° C. the expansion of quartz follows a straight-line 

 law ; between 250° and 470° C. it is necessary to include a 

 term involving the square of the temperature, whilst at 

 500° C. a sudden large increase in the expansibility becomes 

 visible. .•\t this temperature it is probable, as suggested by 

 Le Chatelier, that quartz undergoes a change into a second 

 modification having very different physical properties from 

 those of the ordinary form. The second paper, by Mr. 

 H. D. Ayres, deals with the measurement bv Pulfrich's 

 method of the coefficients of linear expansion of the metals 

 aluminium and silver at temperatures between ioo° and 

 - 184° C. 



The firm of Leybolt Nachfolger in Cologne has recently 

 issued a very complete and interesting catalogue of physical 

 apparatus and fittings sold by them. The book starts with 

 a history of the instrument trade in Cologne during the 

 last century. In its second section we find an account of 

 the construction and fittings of various chemical and 

 physical institutions. It is noteworthy, perhaps, that while 

 the students' laboratory, with its work tables and appliances 

 for experiments, figures prominently in the chemical institu- 

 tions, the arrangements for practical work by the students 

 in the physical laboratories are distinctly less complete. 

 .\fter this follows the catalogue proper, filling some 800 

 large pages, profusely illustrated and admirably arranged. 

 The book will be most useful to the teacher, and is a 

 striking illustration of German enterprise and go. At the 

 same time it is observable throughout that the apparatus 

 is intended chiefly for demonstrations and the lecture-room. 

 The list of electrical measuring instruments, for example, 

 is comparatively meagre, while there are not many examples 

 of the simpler forms of apparatus supplied to an English school 

 laboratory for use by the, students. It is probably the case 

 that such apparatus is less used in Germany than here, but 

 though this is absent the book is full of apparatus of the 

 greatest value and utility. 



A SECOND edition of Prof. Luigi de Marchi's " Meteor- 

 ologia generale " has been published by the house of 

 Hoepli, of Milan. The book has been revised and en- 

 larged. 



A SECOND edition of the " Rural Calendar," fully revised 

 and enlarged, has been prepared by Dr. A. J. Ewart and 

 published by Messrs. Davis and Moughton, Ltd., Birming- 

 ham. The book is a helpful index to observations of 

 animate nature throughout the year, and a guide to 

 gardening and farming operations. It includes an arti- 

 ficial key to the commoner wild British herbs, giving 

 description, common name, scientific name, and natural 

 order. By using this key as plants become available, a 

 good knowledge of common flowers may be obtained. 

 The price of the book is one shilling net. 

 NO. 1846, VOL. 71] 



OUR ASTRONOMICAL COLUMN. 



.Structure of the Coron.'V. — In an interesting paper pub- 

 lishfd in No. 3 (1905) of the Revue ginhaie des Sciences, 

 Dr. Ch. Nordmann discusses the structural details of the 

 solar corona and their causes. In the first place, he shows 

 that the incurvation of the coronal rays cannot b? due solely 

 to the action of gravitation, for the angles which they make 

 with the normals to the limb at the points of their pro- 

 jection are far too small for this theory. 



He then shows that the " minimum " corona, which ob- 

 tains at the time when the solar surface is least disturbed, 

 simply assumes the form natural for it to assume under the 

 action of centrifugal force, if it be granted that the parti- 

 cles forming the coronal streams are exactly balanced in 

 the solar atmosphere — that is to say, if their weight is 

 counterbalanced by the force of the light-repulsion. At 

 times of "maximum," when the solar surface in the sun- 

 spot (i.e. equatorial) region is most disturbed, the 

 local disturbances, and their consequent convection currents, 

 modify the action of the normal centrifugal forces, and thus 

 produce the ahnormal coronas observed at eclipses occurring 

 during periods of maximum solar activity, which, although 

 of the same general form, vary greatly in their detailed 

 features. 



Radiant Point of the Bielid Meteors. — From a num- 

 ber of observations of the Bielids made on November 21, 

 1004, Herr K. Bohlin, of Stockholm, has calculated the 

 radiant point of the shower. 



The resulting position is only about 3° from y Andro 

 med.t, and has the following coordinates : — 



1904 N'ovember 21-33 (Mid-European time). 



{Astronomische Nachrichten, No. 3997.) 

 Brightness of Encke's Comet. — The results of a number 

 of magnitude observations of Encke's comet, made by Herr 

 J. Holetschek, at Vienna, during the present apparition, 

 are published in No. 3997 of the Astronomische Nachrichten. 

 The observations covered the period November 2S-Decembfr 

 27, and, in the table wherein the results are shown, the 

 vertical diameter, the magnitudes of the nucleus, and the 

 magnitudes of the whole comet are given. From the last- 

 named values we learn that on November 25 the magnitude 

 of the comet was go, on December 10, 6, and on December 

 23. 5-3- The value obtained on December 27 was 

 mag. =5.0, but this is queried. 



January Fireballs. — .\ note from Mr. Denning to ihe 

 Observatory (No. 355) shows that the appearance of fireballs 

 during the predicted dates in January was well sustained. 

 On Januarv 14 a bright object was seen by several ob- 

 servers, and on combining the records a radiant point 

 situated in Monoceros at ii9°-F3° was obtained. The 

 height of this fireball ranged from 60 miles over Brecon to 

 29 miles over Abervstwith. Two fireballs were seen on 

 January 27 and one on January 29, thus corroborating the 

 January 28 epoch. One of those on the former date was 

 very bright, and was apparently stationary at ii8°— 18°. 



In February, bright fireballs were seen on February 11, 

 13 and 18, the time of the apparition on the last-named (late 

 being 7h. 15m. a.m., i.e. in daylight. 



Rotation of Jupiter's Satellites I. and II.— During 

 ihe period January 13-20, Dr. P. Guthnick, of Bothkamp 

 Observatory, made a series of magnitude observations of 

 Jupiter's first and second satellites, the period of observation 

 covering about four revolutions of the former and two 

 revolutions of the latter round the planet. 



The measurements were made with a ZoUner photometer 

 attached to the ii-inch refractor. Plotting the values ob- 

 tained on curves having the " anomaly " of each satellite 

 as abscissa and the corresponding apnarent magnitude as 

 ordinate, it was seen that the period of the light-variations 

 coincided with that of the revolution about Jupiter, and as 

 a consequence it seems probable that the periods of revolu- 

 tion and rotation are coincident in each case (Astronomische 

 Nachrichten, No. 4000). 



Orbits of Minor Planets. — In No. 4000 of the Astro- 

 nomische Nachrichten, Prof. J. Bauschinger publishes the 



