September 29, 1904] 



NATURE 



535 



of rattle disease can be readily transmitted by inoculation 

 into rats, the rat-parasite will only develop in its proper 

 hosts. Some curious problems in development are pre- 

 sented bv the life-history of a gregarine found in the blood 

 of a water-snake. 



In the September issue of the American Journal of Science 

 Mr. E. H. Sellards continues his account of the Palsozoic 

 cockroaches, with descriptions of several new Coal-measure 

 types, .\nother article, by Mr. G. R. Wieland, is devoted 

 to the structure of the turtles of the genus Lytoloma, as 

 exemplified by specimens from the Upper Cretaceous of New 

 Jersey. These turtles, it may be mentioned, are character- 

 ised by the backward position of the inner nostrils and the 

 great length of the mandibular symphysis. The author 

 considers that they were specialised for the purpose of feed- 

 ing on shell-fish, and confirms Mr. Lydekker's reference 

 of the English Eocene Chelone planimentuin to the 

 American genus 



Drs. B. L. Robinson and J. M. Greenman continue to 

 publish the results of their examination of Mexican and 

 Central American plants in the first number of the current 

 volume of the Proceedings of the .'\merican .Academy of 

 Arts and Sciences. Mr. M. L. Fernald presents a synopsis 

 of species of AInus, and describes a number of new species 

 from the same countries. 



It is tolerably well known that contact with certain plants, 

 notably species of Rhus and Primula, often causes in- 

 flammation. This may be described as a form of eczema, 

 or in some cases would be more correctly called dermatitis. 

 Mr. J. H. Maiden has made these plants the subject of a 

 short paper which he laid before the Therapeutical Society 

 in March, 1903. 



Since the first description with figures of Melocanna by 

 Roxburgh in 1819, it was known that this genus of bamboos 

 growing in eastern Bengal and Burmah was characterised 

 by the production of a succulent fruit about the size of a 

 pear, and containing one large oval seed ; later it was 

 observed that germination started before the fruit was shed. 

 Only recently has a complete description been forthcoming 

 in the paper which Dr. O. Stapf communicated to the 

 Linnean Society, and which is published in the Transactions 

 (June). The fruit of Melocanna differs from that of ordinary 

 grasses in other respects, because the ripe seed contains 

 no endosperm, the food being stored up in the pericarp, and 

 the collapsed endosperm cells act as a diaphragm. One of 

 the most striking features of the plant is that it forms large 

 jungles or forests, in which after many years of vegetative 

 growth all the plants produce their flowers and fruits 

 simultaneously. 



In view of the discussion of electrical units by the Inter- 

 national Electrical Congress at St. Louis, the Physikalisch- 

 Technische Reichsanstalt publishes in part xxxi. of the 

 Elektrotechnische Zeitschrift a protest against defining the 

 unit of electromotive force by reference to a standard cell. 

 It is maintained that sufficiently large differences exist in 

 the E.M.F. of any one type of cell with differences in con- 

 structional detail to prevent the adoption of such a unit 

 from giving satisfaction. With our present knowledge of 

 standard cells, it is contended, the unit of resistance should 

 he the mercury unit, and current should be defined by refer- 

 ence to the silver voltameter; the unit of E.M.F. is then 

 the derived unit obtained by assuming Ohm's law. 



We have received from the author a reprint of a paper 

 read before the German Physical Society by Mr. L. Austin 

 on the alteration in length during magnetisation of 



NO. 1822, VOL. 70] 



Heusler's magnetic alloys of manganese, aluminium, and 

 copper. It contains a description of a very simple apparatus 

 for measuring minute changes in length, in which the 

 magnifying principle adopted is the reflection of a beam of 

 light from a plane mirror. Besides showing that the alloys 

 increase in length during magnetisation proportionally to 

 the magnetic force, the author describes a peculiar contrac- 

 tion which they subsequently undergo when exposed to a 

 magnetic field of constant strength. The contraction seems 

 to be roughly proportional to the square of the magnetic 

 intensity. 



In No. i8 of the Physikalische Zeitschrift Prof. F. 

 Paschen publishes an experimental investigation of the 

 y rays emitted by radium. These extremely penetrating 

 radiations have hitherto been regarded as most closely allied 

 to the Rontgen rays, but as they carry with them a negative 

 charge which they are capable of imparting to substances 

 that they encounter, it appears more justifiable to regard 

 them as a species of kathode rays. All attempts, however, 

 to deflect the 7 radiations in the same way as the $ rays 

 by means of an intense magnetic field were unsuccessful. 

 Even in a field of 30,000 C.G.S. units a perceptible deviation 

 from a straight line path could not be detected. By carefully 

 measuring the thermal effect of the 7 radiations, the sur- 

 prising result was obtained that the energy of a 7 electron 

 must be at least 3200 times greater than that of a 5 electron. 

 That the 7 rays cannot be the Rontgen effect of the or 

 kathode rays of radium is shown by the fact that their 

 total energy is to that of the /3 rays in the ratio 74 : i- 

 It is concluded, indeed, that the 7 rays carry with them 

 the greater proportion of the energy of radium. 



An improved means of observing the beautiful scintilla- 

 tions exhibited by a sensitive screen under the action of 

 Alpha rays has been devised by Mr. F. H. Glew, 156 

 Clapham Road, S.W. The little instrument, which is 

 called the " Scintilloscope," consists of a simple magnifier 

 of adjustable focus, as in the spinthariscope, but instead of 

 the fixed screen and particle of radio-active substance a 

 small double plate of glass is used. One of these pieces of 

 glass is coated with a radio-active salt, and the other is 

 a radio-sensitive screen. Upon looking at a combination 

 of this kind with the lens the sparkling appearance is very 

 clearly seen. The advantage of this method of observing 

 the effect is that different combinations of radio-active sub- 

 stances and screens can be used. For instance, a sensitive 

 screen placed upon a piece of pitchblende ground flat and 

 polished shows the scintillations very well. Mr. Glew's 

 device provides an effective way of exhibiting the brilliant 

 display produced by radio-activity on sensitive screens. 



In the Proceedings of the American Philosophical Society 

 (vol. xliii. p. 123) Messrs. Edgar F. Smith and F. F. Exner 

 give an account of an elaborate investigation of the atomic 

 weight of tungsten. The authors, on the basis of a critical 

 examination of previous determinations, consider it doubtful 

 whether pure substances have been employed. The mean 

 atomic weight calculated from concordant data obtained by 

 converting the hexachloride into the oxide is 184 04, and 

 by oxidation of the metal 184065. 



Some interesting results have been obtained by F. 

 Garelli and F. Gorni in a study of the isomorphism of 

 organic substances by the cryoscopic method. They are 

 described in the August number of the Gazzetta. Sub- 

 stances may apparently differ very considerably in constitu- 

 tion, and yet crystallise together so as to form a solid 

 solution. Thus, for example, phenyl benzoate, phenyl 

 salicylate, and salicylhydroquinone, which differ by the 



