400 



NA TURE 



[February 22, 1906 



electrons. Prof. Poincare 1 is careful to emphasise the 

 assumptions on which recent views are based, but if the 

 assumptions are c< rrect the final result consists in stripping 

 from matter the attribute of mass by which it is usually 

 defined. Mass appears purely as die result of electrical 

 action, or. in Prof. Point-are's own striking words, " dans 

 ce systeme il n'v a pas de vraie matiere, il n'y a plus que 

 des trous dans 1 'ether." 



Some time ago Prof. Nernst described a simple form of 

 torsion balance capable "I measuring weights of a few- 

 milligrams with an accuracy ol o-ooi milligram. In the 

 current number of the Berichte Mr. H. v. Wartenberg 

 gives an interesting application of this instrument to the 

 determination of the molecular weight of silver vapour. 

 The method used was a modification of the well known 

 apparatus due to Victor Meyer, the vessel being made of 

 iridium, coated internally with a mixture of the oxides of 

 yttrium and zirconium. This iridium vessel was heated 

 in an electric furnace to about 2000 C, the weight of 

 silver used in each experiment varying from 0905 to 

 0322 milligram. The values obtained for the molecular 

 weight of the silver were between 107 and 147, indicating 

 that silver is monatomic. 



Messrs. Dawbarn and Ward, Ltd., have published in 

 their " Home Worker's " series a little book by Mr. 

 Joseph E. Dangerfield on " Brass and Iron Founding." 

 The price is is. 6d. net. 



The " Swincam " camera stand enables a camera to be 

 fixed on the tripod in almost any position, so that photo- 

 graphs can be taken in situations which present insur- 

 mountable difficulties with ordinary stands. A revised 

 pamphlet showing some of the possibilities and performances 

 of this speciality in tripod stands has been issued by the 

 maker, Mr. W. Butler, Southport. 



Messrs. Whittaker and Co. have published a second 

 edition of Mr. S. R. Bottone's " Radiography anil the 

 X ' Rays." The book was reviewed in our issue of 

 July 28, 1898 (vol. lviii. p. 202); and it is only necessary 

 to say here that recent improvements in Rontgen-ray 

 apparatus, and interesting matter connected with the 

 therapeutic effects of the rays, are dealt with in the new 

 edition. 



OUR ASTRONOMICAL COLUMN. 



Comet 1906a. — The following is taken from a continu- 

 ation of the daily ephemeris for comet 1906a (Brooks), pub- 

 lished by Herr M. Ebell in No. 407, of the Astronomische 

 Nachrichten :— 



,0. 



Epkem, 



.(true) 



.s- I2h. M.T. Berlin. 



{(true) logr 



Feb. 22 ... 6 45 35 ... +78 30 ... 02047 •■• 0-0024 ... 082 



24 ... 6 21 29 ... +75 12 ... 02094... 00150 ... 076 



26 ... 6 7 28 ... +71 59 ... 0-2140 ... 0-0288 ... 0-69 



28 ... 5 58 38 ... +68 55 ... 0-2187 •■- o'°435 ... 0-64 



Mar. 2 ... 5 52 47 ... +66 1 ... 0-2234 ... 0-0589 ... 0-58 



4 ... 5 48 50 ... +63 19 ... o 22S2 ... 0-0748 ... 0-53 



It will lie seen from the above that tin- comet is now 

 travelling rapidly down tie- constellation Camelus towards 

 Perseus, and is becoming much fainter. 



A set of parabolic elements <»! the orbit of this object 

 has been computed by M. E. Maubant, and appears in 

 No. 6 (1006) of the Comptes renjus. 



Comet 1905c. — Photographs of Giacobini's comet (1905c) 

 obtained at Greenwich early in January showed that the 

 magnitude was about 30, and that this object had a tail 

 about 2 in length. 



A note in the February number of the Bulletin tic la 

 Socie'te astronomique de France quotes M. (ciacobini, who, 

 in a letter Oi a correspondent, slated that the comet was 

 visible to the naked eye during the whole week preceding 

 January 0, and that it then had a tail about i c in length, 

 the position angle of which was 45 . The nucleus was 

 estimated as being of the second or third magnitude. The 

 nearest approaches i>! ibis object to the earth took place 

 on January and February 2, the respective distances 

 being i-io2 and 1 1 50 astronomical units. Its distance from 

 the sun at perihelion was 02154 unit. 



The Apparent Enlargement of the Moos at the 

 Horizon. — In the Archives de Psychologic (vol. v., No. 18, 

 October, 1905) M. Ed. Claparede publishes an interesting 

 paper on the causes which produce the impression that the 

 sun, moon, and other celestial bodies are larger when near 

 to the horizon than when seen .it the zenith. 



After discussing a number of theories propounded by 

 previous writers on this subjec t, from Aristotle onwards, 

 he examines several possible causes, and recounts the 

 results of various experiments he has made whilst consider- 

 ing the matter. 



Finally, he arrives at the conclusion that when we see 

 the moon, or sun, at the horizon, we are surprised into 

 believing it to belong to things terrestrial — to come into 

 the 1 lass of objects which tue by far of the greatest interest 

 to us. As such we notice it with much greater attention, 



NO. 1895, VOL - 73] 



and for this reason overestimate its size. When at the 

 zenith the moon is of little interest in comparison with the 

 terrestrial objects which belong to our daily life, and we 

 therefore think of it as relatively unimportant ; conse- 

 quently we underestimate its size. This correlation of 

 importance and size is always common, and, as tin illus- 

 tration of it, M. Claparede quotes the fact that boys are 

 always astonished when they learn for the first time that 

 Napoleon was below the average height. 



M. Claparede used the illustration we reproduce, in his 

 experiments with individuals. Covering one of the moons 

 shown, he asked his subjects to draw the other one the 

 same size, and then asked them to draw the second whilst 

 the first was covered. Of twenty couples of drawings thus 

 -I, from thirteen subjects of all ages, the moon at 

 the horizon was shown as the greater on fourteen, as 

 equal on five, and as less on one. The greatest difference 

 was shown on two drawings l,\ the same boy, where the 

 moon was 9 mm. (horizon) and 45 mm. (raised) re- 

 spectively, the actual diameter on the copy being 45 mm. 



M. Claparede's paper may be obtained, as a separate 

 brochure, from MM. Kiindig et Fils, Geneva, price 

 1 franc. 



Magnetic Observations during the Total Eclipse of 

 the Sun. — We have received from Father P. Cirera, of 

 the 1'Ebre Observatory, an extract from the Comptes rendus 

 giving an account of the magnetic records obtained at 



