October ii, 19 17] 



NATURE 



105 



supply of which is necessary with the design of sur- 

 face-combustion apparatus at present in use. 



An article on "'Coal-gas for Motor Vehicles" (Jiimes 

 Engineering Supplement, August 31) gives some 

 li^ures indicating the effect of compressing coal-gas on 

 i!> calorific value. It seems that a suitable pressure 

 uDuld probably not exceed 300 lb. per sq. in. If this 

 i-, loo high for use in a house, the gas could be passed 

 through a reducing valve before entering any group 

 of houses. 



Briefly, high-pressure gas would be supplied to a 

 group of districts with reducing valves where neces- 

 sary, just as a high-tension electric supply has trans- 

 formers placed where required. 



(2) As the gas would be supplied in bulk, its com- 

 position in any one large district would be uniform, 

 thus facilitating the adjustment of the flameless com- 

 busters. In fact, they could be standardised, and sent 

 out ready for use from a central depot for each large 

 district. The combusters would have to be fool-proof; 

 perhaps by arranging to have adjustments only pos- 



ible by the use of special tools. 



(3) It is obvious that a considerable amount of ex- 

 perimental work is necessary, but the benefits to the 

 :ommunity would be so great that it appears worth 

 while starting these experiments as soon as possible. 

 Cheap heating cornbined with absence of smoke is 



,orth trying for. 



(4) It is presumed that the gas would be distributed 

 through weldless steel tubes, so far as possible, above 

 ground for convenience of repair, etc., and along rail- 

 way tracks where possible. K, C. Browning. 



31 Boundary Road, St. John's Wood, N.W.8, 

 September 16. 



P.S. (October 7). — ^A supply of high-pressure gas 

 would be of great value to firms running a service of 

 industrial vehicles, the gas being much cheaper than 

 petrol, and the pressure expediting the filling of the 

 containers. 



Prof. Browning's letter raises a number of prac- 

 tical points which deserve attentioji. 



My former letter was mainly concerned with the 

 onservation of a great national asset. Prof, Brown- 

 ng deals with the matter in the interest of the gas 

 ^KX)nsumer. 



(i) It is impossible to estimate the amount of coal 

 nd labour which are wasted every day in keeping up 

 housands of little domestic fires to boil an occasional 

 ettle, or the saving of coal and labour which a supply 

 f cheap gas would bring about, but they would cer- 



inly be very great. 



I am sorry not to have kept in touch with Prof. 



ne's later experiments, but they are undoubtedly 

 >n the right lines. The key to successful heating is 

 adiation, and the amount of heat radiated from a sur- 

 ace increases very much faster than the temperature. 

 'f, therefore, the principle of surface-combustion can 

 le applied to domestic heaters, there should be a great 

 [ain in comfort, even with a lesser consumption of 



|as. 



It is interesting to contrast the enormous strides 

 ^hich have been made of late years in the efficiency 

 if methods of lighting (both gas and electric) with the 



mparative stagnation in the field of domestic heating. 



rue, the margin of waste in the latter has not been 

 rly so great as in the case of the former, but there 



still plenty of room for economy, and Prof. Bone's 



iperiments seem to point the way. 



(2) It will be convenient to deliver the gas from the 

 Ifields at a high residual pressure, and it will be 



ite feasible to distribute it at high pressure if this 



ould be considered desirable. It is a much simpler 



iatter to confine gas at a pressure of 220 lb. than elec- 



NO. 2502, VOL. 100] 



tricity at 220 volts, and the pressure of the gas could 

 be utilised to deliver air to the surface-combusters. 



(3) A good deal of experimental work will be re- 

 quired to solve the practical problems involved. The 

 enteiprise of our great gas companies will doubtless 

 be equal to the occasion. 



(4) The question of rights of .way will demand very 

 careful consideration. Weldless steel tubes present 

 many advantages, but the question of overground v. 

 underground pipe lines can scarcely be settled offhand. 



Arthur J. Martin. 

 University Hall, Carlyle Square, Chelsea, S.W.3, 

 September 29. 



The Harvest Moon. 



The harvest moon is usually stated to be the full 

 moon nearest in date to the autumnal equinox, and to 

 be distinguished by the peculiarity that tor a few suc- 

 cessive evenings the retardations of the times of rising 

 are at a minimum. 



Now, applying these tests to the full moons of Sep- 

 tember I and 30 of the present year, it will be found 

 that they are inconsistent. The retardations at Green- 

 wich, from August 29 to September 4, are, in minutes, 

 30, 22, 21, 19, 21, 22, an average of 22^ minutes; 

 but, from September 27 to October 3, are 23, 20, 20, 

 22, 25, 31, an average of 237} minutes, so that for the 

 full moon of September i the retardation was slightly 

 less than for the full moon of September 30, although 

 the latter was much nearer the date of the equinox. 



Possibly Sir George Greenhill, in his very interesting 

 article (Nature, September 27, p. 67), overlooked this 

 peculiarity, due, of course, to the fact that the moon 

 was at the first date much nearer the ascending node 

 than at the second date. I may add that the average 

 daily retardation in the time of rising is 50^ minutes, 

 the average length of a lunar day being 24h. 502m. 

 In conclusion, I find that the interval between tw6 

 successive returns of the moon to the meridian may be, 

 in extreme cases, about twelve minutes less, and about 

 seventeen minutes more, than the average. 



C. T. Whitmell. 



Invermay, Hyde Park, Leeds, September 28. 



Folk-iore and Local Names of Woodlice. 



Amonst the readers of Nature there are rnany, I 

 feel sure, who are interested in the folk-lore and local 

 names of the members of our fauna. May I appeal 

 to such for any information bearing upon the heading 

 of this letter? 



Already nearly one hundred local names, such as 

 bibble-bug, chisel-hog, cud- worm, palmer, lock- 

 chester, slater, tiggy-hog, etc., have been obtained, and 

 the districts noted in which such are in use. Celtic 

 and Gaelic names are particularly desired. 



AV .ALTER E. COLLINGE. 



The L'niversity, St: Andrews, October 4. 



The Convolvulus Hawk-moth. 



In reply to Mr. C. E. Robson's letter in Nature of 

 September 20, I write to say that I have lately become 

 the possessor of two specimens of Sphinx convolvuli. 

 The first one was caught at Deal on September 12 ; 

 it shows signs of wear, and had probably come over 

 from the Continent. The second I took myself in 

 Queen Elizabeth's Walk, Stoke Newington, London, 

 N., on September 22. It was in perfect condition, and 

 had every appearance of having just hatched 

 out. It was resting on a wall close to some 

 bindweed, and it seems probable that it was bred there. 



J. Laker. 



8 .\llerton Road, N.16, October 4. 



