5^54 



NATURE 



[March 30, 191 1 



the very sparse occurrence of the carbon and the lack of 

 agreement between the amounts of carbon and gold. 

 'Ihus, according to Mr. Ilorwood's table of analyses of 

 samples from the West Reef dyke of the North Randfon- 

 tein Mine (Ap|K,'ndix D, p, 92), one of the three specimens 

 containing the highest percentages of carbon had the 

 smallest weighable quantity of gold, and of the two speci- 

 mens with the highest percentage of gold one had only a 

 Irace of carbon, and the other was one of the lowest in 

 carbon in the whole scries. Mr. Horwood bears tresh 

 testimony to the fact that throughout the Rand good 

 values are almost invariably found when pebbles of a 

 pinkish-brown quartzite occur in the banket. 



To the Sitzungsberichte of the Vienna Academy of 

 Sciences (July, lO'o), Dr. W. Schmidt contributes a 

 lengthy investigation on thunderstorms and squalls, rapid 

 rises of barometric pressure. The work is divided into 

 two parts : — (i) the observations and results of sixteen 

 months' records of the variometer at the Central Meteor- 

 ological Office at Vienna, especially with reference to the 

 ■cases of rapid rises mostly caused by squalls, &c. ; (2) ex- 

 perimental investigations of . the incursion of heavier 

 (colder), under lighter (warmer) air, and its effect on the 

 Tormation of the squalls. The latter subject constitutes 

 the essential part of the whole investigation, and this in- 

 flowing of the cold air, the author states, never takes 

 place in the form of a simple wedge, but the front portion 

 has the shape of an uplifted head (illustrated in the 

 •diagrams). " This head, with the currents that it causes. 

 Is the core of the squalls and thunderstorms. In these we 

 cannot therefore speak of an actual whirl with horizontal 

 axis." He considers that another theory must be substi- 

 tuted for the old one, which would explain all the pheno- 

 mena in squalls essentially by the motions which, under 

 the influence of gravity, must take place from the juxta- 

 position of two layers of air at different temperature. 



The Zeitschrift fiir den physikaltschen und chemischen 

 Unterricht issues from time to time special parts dealing 

 with the method of teaching and the philosophy of science. 

 In a part of 120 pages, which has recently appeared, Dr. 

 H. Liidtke, of the Modern High School (Real-Gymnasium), 

 Aitona, gives details of a course on electrical oscillations 

 and the electromagnetic theory of light suitable for the 

 older pupils in modern high schools. It includes construc- 

 tion of a Tesla transformer, experiments to show the re- 

 pulsion of a metal disc and other mechanical actions of 

 the currents obtained, together with their thermal, optical, 

 ■chemical, and physiological effects. The portions of the 

 theory of alternating currents necessary for the study of 

 the theory of light are then introduced, and are followed 

 by experiments on electrical oscillations, their interference, 

 •diffraction, and polarisation. The course is well thought 

 out, both theoretically and experimentally, and will com- 

 mend itself to those high-school teachers in this country 

 Avho have the time and apparatus necessary for the pre- 

 paration of a course on the subject, and the pupils capable 

 of benefiting from such a course. 



.'\ SMALL portable photometer, known as the " Holophane 

 Lumeter, " for determining the luminosity of surfaces, has 

 been constructed by Messrs. R. and J. Beck. It measures 

 8i by 2j by 2f inches, and is divided into two chambers, 

 the first of which contains a small electric lamp run from 

 two storage cells. The light from this chamber, the walls 

 of which are painted white, passes through a small open- 

 ing into the second chamber, which contains the circular 

 photometer screen. The matt-white surface of the 

 screen is viewed through an eye-piece inserted obliquely 

 NO. 2 161, VOL. 86] 



into the side of the chamber. The surface the lum 

 of which is to be deterniined is seen through an (>]> 

 in the centre of the icreen, and a corresponding one in 

 the end of the chamber. Two sectors, one notched, the 

 other plain, can be moved over the aperture between the 

 two chambers until the brightness of the outer part of the 

 photometer screen is equal to that of the central part. The 

 luminosity of the surface viewed is read on two scales out- 

 side the box, over which two pointers connected with the 

 sectors move. One scale reads up to o-i and the other to 

 i-o candle foot. By means of dark glass screens inter- 

 posed in the path of the light coming from, the surface 

 tested, the readings may be extended up to 100 candle feet. 

 The instrument is standardised by being made to read 

 10 when directed to a white surface i foot away from a 

 standard candle. 



Messrs. Newton and Co., 3 Fleet Street. -t 



issued a new price-list of X-ray, high-frequency, and 

 electro-medical apparatus. The X-ray apparatus shows 

 evidence of development in several directions. The 

 " Snook " apparatus consists essentially of a step-up trans- 

 former immersed in a tank of oil. The primary receives 

 alternating current from a dynamo, which is worked from 

 the electric supply mains. A simple mechanical high- 

 tension commutator is placed in the secondary circuit, and 

 renders the secondary charge unidirectional. The axis of 

 the commutator is continuous with the axis of the dynamo, 

 and thus perfect synchronism must necessarily result. 

 From a convenient switch table the secondary discharge 

 can be regulated from a very small to a very large one. 

 The introduction of this apparatus has led to modifications 

 and improvements in all other forms of generating 

 apparatus ; coils have been constructed with a large 

 amount of metal in the core, and a comparatively thickly 

 wound secondary, so as to be capable of giving large dis- 

 charges comparable with those obtained from the secondary 

 of the " Snook." Mechanical and electrolytic interrupters 

 have also been developed and enlarged in such a way as 

 to enable large primary currents to pass through them. 



No marked development has taken place in X-ray tubes 

 in recent yeai-s, but there are several on the market now 

 which are able to stand a heavy secondary discharge, and 

 thus enable skiagrams of the thicker parts of the body to 

 be taken with very short exposures. The accessory 

 apparatus described in Messrs. Newton and Co. 's list re- 

 ferred to above includes certain devices for the protection of 

 the operator. One of these is a lead-lined cabinet in which 

 the observer and one or two others can incarcerate them- 

 selves while the X-ray tube is in action. The switch- 

 board is placed in the cabinet. A cabinet of this sort was 

 introduced some years ago by Dr. Albers-Schonberg, of 

 Hamburg. Its utility is confined to cases in which X-ray 

 treatment is to be given, or an X-ray photograph is to 

 be taken, though it is obviously of no use for fluorescent- 

 screen observation, a most important part of diagnostic 

 X-ray work. For protecting the operator during 

 fluorescent -screen operations. Dr. Jordan's adjustable lead- 

 lined screen is illustrated, and also the revolving saddle 

 upon which the patient is seated during the use of this 

 lead-lined screen. Several old patterns of tube stand are 

 still figured in which the X-ray tube is not enclosed in a 

 protective shield or box. Thus on p. 69 two naked X-ray 

 tubes are shown supported by a single jointed clamp. No 

 X-ray tube should ever be used in this unprotected state 

 at the present day, and it would have been better to have 

 omitted such stands from the price-list, as they are a 

 source of danger to those who use them. 



