February 23. 1899J 



NA TURE 



405 



publicatiun of the second part of Gortlan's " Vorlesungen iiber 

 Invarianlentheorie" in 1887. Goidan's famous theorem is on the 

 finiteness of the form-system of one or more binary forms. After 

 a slight introduction, the subject is discussed under six lieads, 

 viz. Mertens' demonstration and Hilbert's first proof of the 

 theorem ; Hilbert's general proof for forms in « variables ; 

 Deruyts' researches in enumeration of covariants of given 

 characteristics ; Hilbert's theorem upon syzygies of higher orders ; 

 miscellaneous topics ; and the writer winds up with desiderata 

 and remarks upon courses of instruction. It will be gathered 

 from the above selection of headings that the report is likely to 

 be useful to students. There are numerous references, which 

 we hope are more accurate than the following footnote on the 

 first page, which cites Sylvester's proof of the theorem ; thus 

 " Proc. Lond. Math. Soc., vol. 27 (1878), p. 11-13." There is 

 a remarkable muddle here. Vol. xxvii. gives Proceedings of 

 Session 1895-6, the Proceedings of 1878 appear partly in vol. ix. 

 and partly in vol. x., and no reference to such communication 

 occurs in the index to the first twenty volumes of the Pro- 

 cceilings. — Miss C. A. Scott discusses Holgate's translation of 

 Reye's " (jeometrie der Lage. " — Prof. M. Bocher gives an 

 account of Burkhardt's " Funktionentheoretische Vorlesungen," 

 vol. i. , einfiihrung in die Theorie der analytischen Functionen 

 einer complexen Veriinderlichen. The little work is said to be a 

 useful introduction not merely to those parts of the theory which 

 have been long classical, but also to the many other important 

 developments of the last thirty years. — An extensive review of 

 Darboux's " Le9ons sur les Systemes orthogonaux et les 

 coordonnees Curvilignes," by Prof. E. O. Lovett. which follows, 

 bristles with references to original memoirs. — Prof. J. Pierpont 

 warmly commends the new Mathematical Encyclopiedia, the 

 success of which he regards as being mainly due to the genius, 

 energy and courage of a single man, Felix Klein. — Errata, 

 Notes ^which are fuller than ever under Prof. Lovett'.s care), and 

 new publications close the number. 



Bollettino delta Socielii Sismologica Italiana, vol. iv. , 1898, 

 No. 6. — Vesuvian notices (January-June 1898), by G. Mercalli. 

 Describes the state of the volcano during each month, adding 

 notes on the changes in the depth of the crater and the excen- 

 trie eruptive apparatus. — Correction [of an error in copying] 

 in the report of the geodynamic observatory of Casamicciola 

 (Ischia) on the Indian earthquake of June 12, 1897, by G. 

 Grablovitz. — Reply to the same, by G. Agamennone. — Mode 

 of utilising already exhausted Dalle- MoileAxy piles : new " Guz- 

 zanti " pile, by C. Guzzanti. — Notices of earthquakes recorded 

 in Italy (October 2-November 26, 1897), by G. Agamennone, 

 the most important being the earthquakes of Porto Maurizio 

 (October 12), the Marches (October 28), Tuscany (November 

 1-2), and Latium (November 6 and 13), and distant earthquakes 

 of October 1S-19, 20, 23, and November II. 



In the Journal of Botany for January, Mr. Herbert Goss 

 gives an account of the finding of Orckis cruenta in Cumberland, 

 already alluded to in these columns. — In the number for Feb- 

 ruary, Mr. G. S. West commences a list of the Alga flora of 

 Cambridgeshire, a comparatively unworked ground. The list 

 will comprise 409 species, 35 of them new to the British Isles, 

 and 9 new to science, including a new Bttthochaete and a new 

 Oedogoniiim. — Mr. H. C. Hart commences an account of a 

 botanical excursion through the little-known West of Donegal. 

 — Messrs. Britten and Boulger complete their first supplement 

 (1893-1S97) of their Biographical Index of British and Irish 

 Botanists. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, February 9. — "On the Reflection of 

 Kathode Rays." By A. A, Campbell Swinton. Communicated 

 by Lord Kelvin, F.R.S. 



The author has investigated the para-kathodic rays, so called 

 by Prof S. P. Thompson, which in a focus tube proceed from 

 the front surface of the ami kathode, and cause the green fluor- 

 escence of the glass. By means of a tube in which these rays 

 cast the shadow of a wire upon the opposite end of a tubular 

 annex he has studied their magnetic deflection, and finds it to 

 be in a similar direction to that of kathode rays. By means of 

 another tube containing a small Faraday cylinder, into which 

 some of the para-kathodic rays were caused to pass, he has de- 

 termined that the para-kathodic rays carry negative charges. Trie 

 author has previously shown that para-kathodic rays produced 



NO. 1530, VOL. 5q] 



Rontgen rays, where they strike the glass ; they also produce 

 green fluorescence, hence he concludes that para-kathodic rays 

 are simply reflected kathode rays. 



The mechanical force exerted by these reflected kathode rays 

 appears to be exceedingly small, and is insufficient to account 

 for the inverse rotation of radiometer wheels, which, as de- 

 scribed l)y the author in the Pliit. Mag. for October 189S, 

 occurs when the wheels are placed just outside the kathode 

 stream. Indeed, all experiments designed to produce rotation 

 by the impact of reflected kathode rays failed, and in some 

 cases the wheels were found to rotate most persistently in a 

 contrary direction, showing that whatever be the cause of such 

 inverse rotation, it is more potent than the force of impact of 

 the reflecied rays. 



The reflection of kathode rays is largely diffuse, but not alto- 

 gether so ; experiments with a polished concave platinum re- 

 flector, capable of rotation, gave under certain conditions dis- 

 tinct visual evidence of true specular reflection, with equal 

 angles of incidence and reflection. In addition to the specularly 

 reflected rays the anti-kathode reflector was also found under 

 certain conditions to give off a well-defined beam of other rays 

 normal to its surface, which caused fluorescence of the glass. 

 The exact nature of these normal anti-kathode rays calls for 

 further investigation. 



The author has studied and quantitatively measured the 

 eleclric charges carried by reflected kathode rays for different 

 angles of incidence and reflection by means of special apparatus. 

 A tube was constructed for this purpose, in which a polished 

 flat platinum reflector could be set at different angles to the 

 incident kathode rays. This tube was fitted with a movable 

 Faraday cylinder which was capable of rotation round the 

 reflector, so that throughout a single plane the whole field 

 traversed by the reflected kathode rays could be explored. The 

 amount of negative charge imparted to the movable Faraday 

 cylinder at different positions, and with different angles for 

 the reflector, were measured both by a reflecting galvanometer 

 and also by a quadrant electrometer. Many complete series of 

 observations for different positions both of reflector and cylinder 

 were made and all agree in showing that the field of reflected 

 kathode rays is not uniform, but increases more or less gradually 

 on both sides up to a maximum, which always occurs almost 

 exactly at the point that makes the angle of reflection equal to 

 that of incidence. 



Further experiuients show that the amount of charge carried. 

 by the reflected rays increases as the incidence is made 

 more slanting, and that the electrification of the reflector itself, 

 which is strongly negative when the incidence of the primary 

 kathode rays is normal, gradually falls to zero as the incidence is 

 made more slanting, until with very slanting incidence the 

 electrification becomes slightly positive. 



The author compares this result with that described by him 

 in the Poy. Soc. Proc. , vol. Ixiii, pp. 434-435, viz. that kathode 

 rays which .strike the anti-kathode normally, are more efficient 

 in producing Rontgen rays than those which impinge upon it 

 very much on the slant. 



The author points out that these results support the view 

 that the Rontgen rays are actually due to the electric charges 

 carried by the kathode ray particles being imparted to the anti- 

 kathode. 



Entomological Society, February I. — Mr. George H. 

 Verrall, President, in the chair. — Mr. Champion exhibited 

 specimens of an interesting species of Fulgoridie, Atatanta 

 aurico/na,Jiurm. , recently received from British Honduras, and 

 stated that he had found Lepidopterous larva; in the white 

 waxy matter attached to the body of an allied species, Encho- 

 pliora stetlifer, Burm. , of which he exhibited a specimen,, 

 together with a larva taken from it. He also showed numerous 

 specimens, and pointed out certain peculiarities, of both sexe.*; 

 of an undescribed species of Apionierns (Family Reduviids) 

 found by himself in Chiriqui. — Mr. Tutt exhibited on behalf of 

 the Rev. G. H. Raynor a large series of Spilosoma lubricipeda, 

 Linn., to show that the extreme aberrations of this species 

 could be produced by inbreeding from comparatively normal 

 forms. He then exhibited a number of closely allied forms of 

 Anthrocera, received from M. Oberthiir of Rennes, and com- 

 prising, among others, A. medicaginis, Dup., A. medicaginis, 

 Bdv., A. cliaron, Dup., and A. cfiaron, Bdv. The first two of 

 these, as probably also the fourth, he referred to medicaginis, 

 Bdv., considering them to be possibly forms of Aniltrocera 

 tonicerca ; while the specimens of .4. c/iaron, Dup., were, he 



