December 30, 1920] 



NATURE 



577 



were followed by two theodolites 4290 ft. apart, and 

 also by a range-finder. The results obtained from the 

 range-finder are said to be very much less accurate 

 than those given by the two theodolites, both the 

 hfights and the distances by the range-finder being 

 (insistently low by about 10 per cent. 



Mr. N. a. .Vlle.v read an interesting paper on the 

 < urrent density in the crater of the carbon arc to the 

 Physical Society on December 10. By using an arc 

 between a positive carbon and two negative carbons 

 in the same plane, but inclined to the positive at 

 KX)", he found that the crater was a circular plane 

 which could be easily focussed on the screen and 

 Miurately measured. The distance between the 

 arbons corresponded to the largest " silent " current. 

 I en minutes were allowed to elapse before a reading 

 was taken, so that the crater had time to assume its 

 normal size. Under these conditions Mr. Allen found 

 that with a ma.ximum inaccuracy of about i per cent, 

 ihe area of the crater in millimetres was equal to the 

 current in amperes multiplied by 1-34. The experi- 

 ments were made with currents varying between 

 2-5 and 10 amperes. 



.\ THIRTY-P.AGE pamphlet on "Optical Methods in 

 Control and Research Laboratories," just published 

 by Messrs. A. Hilger, Ltd., will prove of great use 

 to works physicists and chemists concerned in the 

 determination of the refractive indices, absorptions, or 

 optical rotatory powers of materials. As a rule, such 

 determinations must be made on direct-reading instru- 

 ments, but it is desirable that the observer should 

 understand the principles of the instrument which 

 he uses, and be able to tell at once when it 

 has gone wrong and to set it right. The pamphlet 

 contains tables of the ranges and sensibilities of the 

 different types of instruments and gives numerous 

 references to books and memoirs in which further 

 information may be found. 



The October quarterly number of the Journal of 



the Society of Glass Technologj- contains an article 



by Dr. \V. E. S. Turner on " Some Developments in 



the Study of Glass Technology in the Year icjit^io." 



Dr. Turner states that during the war this country 



k|>roduced chemical glass " second to none in the world 



far as chemical resistance was concerned " ; and 



hat as regards optical glass, glasses superior to 



[those produced at Jena have been made on a com- 



Imercial scale in this country, and also in very great 



[variety. If it were a question of quality only, Dr. 



Turner adds, then we could very reasonably hope to 



maintain our market intact. But the existing rates 



of exchange in certain foreign countries operate to 



the disadvantage of the industry in this country. 



The article reproduces the fourth annual report of 



the Delegacy for Glass Research, from which it 



appears that, besides a considerable output of research 



work, much has been done to resuscitate the educa. 



lionnl work of the University of .SheflieUI in the 



department of glass technology. .An appendix to 



th<' report gives a list of Ihe researches either planned 



or already in progress. Many of these r««carrhes arc 



■" fields in which other »ci«nlific bodies, such as the 



itional Physical laboratory, the British Scientific 



NO. 2670, VOL. 106] 



Instrument Research Association, and the Glass Re- 

 search Association, are also working. The journal 

 contains, besides several interesting papers com- 

 municated to the society, including one by Dc. 

 George H. Miles on "The Human Factor in In- 

 dustry," a useful section of abstracts and reviews. 



The report on the Keating of buried electric cables 

 which was presented to the Institution of Electrical 

 Engineers on December 17 is of interest to men of 

 science as well as to engineers. The thermal 

 problems in connection with the cables are those 

 principally considered, and important results have 

 been obtained. For instance, it is proved that the 

 thermal conductivity of the paper insulation used in 

 high-tension cables is about three times as great 

 as that of paraffin wax and practically constant. 

 Hence to determine the temperature of the inner cores 

 of the cables carrying given currents all that is neces- 

 sary is to determine the thermal resistance of the 

 earth in contact with the lead sheath. The thermal 

 conductivity of earth containing 15 per cent, of 

 moisture was found to be five times greater than 

 that of the paper insulation. Hence by elementary 

 calculations it is now possible to calculate the tempera- 

 ture rise of cables carrying given currents when laid 

 in certain soils. .\ curious result found by one of the 

 experimenters was that a cable when buried 4 ft. 

 under the ground heated more than when it was only 

 buried i ft. Hence the cooling by air convection of 

 the heated ground in the latter case must have been 

 appreciable. It is of interest to notice the close con- 

 nection between the problem discussed in this report 

 and the corresponding problems in connection with 

 the electrostatic capacity and the current-flow in 

 cables. Kelvin pointed this out eighty years ago. 



A PAPER read by Engr.-Comdr. C. J. Hawkes 

 at the meeting of the North-East Coast Instttu> 

 tion of Engineers and Shipbuilders on Novem- 

 ber 26 contains a great deal of information 

 derived from experiments on the injection and 

 combustion of fuel-oil in Diesel engines. Th-^se 

 ixpcriments were carried out at the .Admiralty Kn- 

 ginwring I-.-iboratory on both the solid-injection and 

 air-injection systems. The engine experimented upon 

 was a single-cylinder four-stroke engine having a 

 piston of aluminium alloy, 14^ in. diameter by 15 in. 

 stroke, developing 100 brake-horse-power at 380 

 revolutions per minute. The paper is very long, and 

 it is possible to make reference to one or two points 

 only. One of the later tests with solid injection 

 gave an average fuel consumption of just under 

 0-4 lb. per brake-horse-power per hour when develop- 

 ing 100 brake. horse-power at 380 revolutions per 

 minute. The sprayer usetl in this test had five 

 (>-<)i6-in. holes, with flats, and a fuel-valve roller 

 clearance of o-ooj in. In this test the piston had 

 been fitted with an obturator ring, which proved 

 beneficial. In all the tests the best all-round re.sults 

 wore obtained from this sprayer. Taking the fuel, 

 oils experimented with in these tests, it has been 

 found that up to about 100 lb. per sq. in. mean 

 indicated pressure the fuel consumption with solid 

 injection is approxitn.iidv the same as, the fuel con- 

 sumption with air inji-rtion at the same power and 



