June i 7, 1922] 



NA rURE 



793 



and may have represented the prey of man, or have 

 been introduced by accident. They vary in age, the 

 author considers, from loo to more than 2000 years. 



Motor Headlights without Glare. — Some re- 

 searches on motor headlights were summarised by 

 Mr. H. S. Ryland at the recent discussion on this 

 subject before the Optical Society (Nature, May 27, 

 p. 694). Mr. Ryland remarked that glare was 

 largely a matter of comparison. Two of the chief 

 factors, the " after image " effect and the regions of 

 insensibility surrounding the image of a bright object, 

 varied with the size of that object. He concluded 

 from his experiments that for a given brightness of 

 the beam, glare varied as the square of the apparent 

 imeter of the course. Mr. Ryland has accordingly 

 signed a lamp with a 2 in. aperture, all the available 

 jht (less about 4 per cent, and the ordinary reflection 

 "ses) being included in the beam, the upper limit 

 which is normally horizontal. Tests on the road 

 )wed that such lamps yielded adequate illumina- 

 and yet could be passed by other road users 

 lOut discomfort. 

 Effect of Stress on the Heat Conductivity 

 Metals. — ^The measurements of Smith in 1909 

 Physical Review, vol. 28, p. 107) and 'those of 

 "mstone in 1916 (Philosophical Magazine, vol. 29, 

 [95) on the effect of stretching on the conduction 

 heat along wires showed that for most of the 

 imoner metals stretching increased the conduction 

 about 7 parts in a million for each megadyne 

 per sq. cm. of stress up to the elastic limit. 

 Lussana's measurements in 1918 of the effect of 

 hydrostatic pressure on the conductivity {Nuovo 

 Cimento, vol. 15, p. 130) gave increases as the pressure 

 increased at approximately the same rate up to 

 pressures of about 3000 megadynes per sq. cm. In 

 the April issue of the Proceedings of the American 

 Academy of Arts and Sciences, Dr. Bridgman 

 gives an account of his recent measurements of 

 the effects of pressures up to 12,000 megadynes 

 per sq. cm. on the heat conductivities of eleven 

 metals. He finds that pressure increases the con- 

 duction in the case of lead, tin, iron, and decreases 

 it in the case of copper, silver, nickel, bismuth and 

 antimony. The rates of change lie between 2 and 

 : 2 parts in a million per megadyne increase of pressure. 

 Regulating Resistances. — A comprehensive 

 catalogue of regulating resistances, ranging from 

 large banks of grid resistances to small adjustable 

 rheostats, has been issued by Messrs. Isenthal and Co. 

 (Denzil\Vorks,Willesden) . The method of construction 

 of a tightly wound single layer of bare wire on an 

 insulating cylinder with a spring sliding contact of 

 ample dimensions moving axially over the wire, is 

 adopted up to quite large sizes for field regulating 

 resistances of the type in which only the regulating 

 hand wheel is in front of the board. These are made, 

 either with a slow motion screw gear, or actuated by 

 wires so that one turn of the wheel covers the whole 

 range. Dimmers for incandescent lighting with the 

 same type of resistance are also illustrated. The 

 large grid type resistances are made up in a variety 

 of forms for different purposes, such as meter caUbra- 

 tion, artificial loads, and other testing work. In 

 many of these, control is effected by putting a varying 

 number of sections in parallel by a circular switch 

 of substantial construction with a moving contact 

 segment, which passes under a series of radially 

 disposed carbon contacts resembling djmamo brushes 

 in holders or the box pattern. 



Viscosity and Flash-point Apparatus. — 

 Messrs. Gallenkamp of 19-21 Sun Street, Finsbury 

 Square, have sent us an illustrated pamphlet describ- 

 ing standard apparatus for determining the viscosity 



NO. 2746, VOL. IO9J 



and flash point. The increasing importance of 

 petroleum products for motor fuel, lighting, heating, 

 and lubricating purposes, together with the fact that 

 the industry is rapidly assuming considerable pro- 

 portions in this country, renders the possession of 

 accurately standardised testing apparatus a matter 

 of great interest, and Messrs. Gallenkamp are to be 

 congratulated on their foresight in putting before 

 the laboratory staffs of the oil refiner and the oil 

 consumer the useful compendium under notice. It 

 is unfortunate that this country, the continent of 

 Europe, and the United States have each developed 

 a type of viscometer which at be st is merely empirical. 

 All suffer from the drawback of a capillary far too 

 short which is difiicult to clean, and none of the 

 instruments give absolute readings. The tables of 

 comparison between the three types. Redwood, 

 Engler, and Saybolt, are only approximately correct, 

 and the range of observations is relatively narrow. 

 Until, however, a universal viscometer has been 

 devised the three instruments mentioned will retain 

 their places. The pamphlet gives instructions for 

 using Redwood's viscometer and might very well 

 have added concise instructions for the operations 

 of the other two. The recently described instruments 

 of Stammer and Michell are also described and quoted. 

 The list includes the well-known flash-point apparatus 

 of Abel, Abel-Pensky, and Cray, and the standard 

 distillation tests of Engler and the British Engineering 

 Standards Association. 



A Crystallographic Index. — " A List of New 

 Crystal Forms of Minerals," by Dr. Herbert P. 

 Whitlock, was issued in April (1922) as a separately 

 bound brochure, from the Bulletin of the American 

 Museum of Natural History (vol. 46, Art. II., pp. 

 89-278). Such a systematic compendium of new 

 crystal " forms " (groups of faces of equivalent value 

 with respect to the symmetry) should prove of great 

 value. Often it is very difficult, when measuring 

 crystals of known minerals from new localities, or 

 crystals exhibiting specially interesting features 

 although from known localities, to be quite sure, 

 on discovering what are apparently new and hitherto 

 unobserved forms, that these forms have in truth 

 never been previously observed. Crystallographic 

 Uterature is now so voluminous and complex, so 

 scattered in so many different publications, that 

 it is a matter of great labour to be thoroughly 

 conscientious in seeking for previous records of the 

 observation of these possibly new forms. Indeed, it 

 frequently happens that such a search is not as 

 thorough as the case requires, and in the actual 

 compilation of this list Dr. Whitlock has found many 

 cases where forms cited as new, and forming the sole 

 subject of a paper supposed to be of original in- 

 vestigation, have proved to have been previously 

 described — and more than once— by other authorities. 

 The scope of the compilation includes the thirty 

 years from 1890 to 1920. The thanks of both 

 mineralogists and crystallographers are due to Dr. 

 Whitlock for so useful a production, which is rendered 

 all the more valuable by the fact that full refer- 

 ences to all the original authorities are given. To- 

 gether with the abstracts of crystallographic papers 

 which are being published by the Mineralogical 

 Society of London, and the lists of new minerals 

 and new forms which from time to time are being 

 included in the Mineralogical Magazine, we have 

 now the material in compact form wherewith to set 

 in order the whole record of crystallographic achieve- 

 ment, and to remove the stigma of " chaotic 

 Uterature " which has been with some truth attached 

 to the Uterature of this subject in the not too distant 

 past. 



