NATURE 



[December i6, 1915 



Viscosity of Cobbler's Wax. 



For slowly damping a vibrating Instrument of im- 

 portance to the Navy, I let a metal knife cut through 

 cobbler's wax, which is just soft enough to be_squeez- 

 able between the fingers. The actual softness or liard- 

 ness of the wax does not greatly matter, but what 

 does matter is its becoming very much softer when its 

 temperature increases from 15° C. to 30° C. This is 

 its defect. I write in the hope that some one of your 

 readers may be able to tell me of a suitable substance 

 which will vary less in its softness as its temperature 

 changes. John Perry. 



25 Stanley Crescent, Netting Hill, W., 

 December 9. 



The Cause of Fluted Weathering. 



Has the cause of fluted weathering, I would like to 

 ask, ever been determined? It differs widely from 

 all other forms of weathering that I have seen or read 

 of. The long, smooth, parallel grooves are met with 

 sometimes on the two sides of a block of limestone 

 when such lies so that there are roof-like surfaces 

 uppermost. On these two sides they frequently corre- 

 spond at the ridge and follow a direct course down- 

 wards unless compelled to curve round some project- 

 ing boss. 



The grooves may be 3 ft. long and of about equal 



Fluted weathering in limestone, Italy. X J. 



width and depth along their whole course. The only 

 specimen known to me in English museums is in the 

 Oxford University Museum, which was got by Prof. 

 W. J. Sollas from the Gemmi pass. I have seen good 

 examples in the Jurassic limestone of Liguria, espe- 

 cially on the west of Finalmarina. Behind Pietra, 

 on the left of the footpath to Ranza, the block, shown 

 in this illustration, with several others, were seen. 

 They were under olive trees, but it seemed impossible 

 for such fluting to be produced by drip, and I wonder 

 whether it could be the result of heavy dews or to 

 some zoning influence. G. Abbott. 



2 Rusthall Park, Tunbridge Wells, December 4. 



Winter Thunderstorms. 



Those of your readers who may observe thunder- 

 storms in the British Isles during the winter months 

 would give great assistance to an investigation of 

 thunderstorms on which I am engaged if they would 

 report by postcard when they observe lightning or 

 thunder during this winter. When sheet lightning is 

 observed at night the time and direction should be 

 given, and a note as to whether many flashes were 

 seen or whether there were only two or three. When 

 NO. 2407, VOL. 96] 



thunder Is heard the time should be given, and the 

 direction of the storm ; it should also be stated whether 

 lightning was seen and whether rain occurred. Much 

 useful information might be gained from winter 

 storms, but as thunderstorms may be very local they 

 may sometimes be missed by the official observers ; I 

 should therefore gladly welcome help from anyone who 

 is good enough to send me Information. It Is obvious 

 that only winter storms can be dealt with In this way ; 

 I would therefore ask those who are willing to help 

 to send information up to March 31st only. 



Charles J. P. Cave. 

 Meteorological Office, South Farnborough, Hants, 

 December 9. 



The Quadrantid Meteors. 



The ensuing display of these meteors occurs in the 

 absence of moonlight. If the maximum continues to 

 be at about the same position of the earth's orbit as 

 formerly it will be in the early evening of January 3, 

 which would be a convenient time for observation, 

 although the radiant point is comparatively low then, 

 the morning displays being the best. 



T. W. Backhouse. 



West'Hendon House, Sunderland, December 6. 



LABORATORY ELECTRIC FURNACES. 



MANY of the modern methods of chemical 

 analysis involve the use of furnaces for the 

 prolonged heating of materials ; for example, the 

 determination of carbon in steel, the carrying out 

 of sealed-tube operations, etc., may be cited. Until 

 recently, gas furnaces have almost exclusively 

 been used for such purposes, but it seems probable 

 that these will be largely replaced, in the future, 

 by the improved types of electric furnace which 

 are now obtainable. The electric furnace offers 

 many advantages over the gas furnace, particu- 

 larly in cases where it is desirable to maintain a 

 constant temperature for any length of time. 



The introduction of the comparatively new high 

 resistance alloys of small temperature-coefficient 

 has greatly simplified the construction and work- 

 ing of wire-wound furnaces. Such a furnace 

 consists in its essential details of a tube of re- 

 fractory material such as fireclay, alundum, or 

 silica, upon which is wound a suitable length of 

 the wire or strip ; the tube is then supported in 

 a case, the intervening space being filled with a 

 material of low thermal conductivity, magnesia, 

 for example. To ensure a long life and satis- 

 factory running, attention must be paid to certain 

 constructional details. The principal of these 

 are : — (i) That the wire employed is as thick as 

 possible, consistent with the dimensions of the 

 tube and the voltage of the supply on which it is 

 intended to be used ; (2) that the wire is effectively 

 protected from oxidation by preventing the access 

 of air, the winding being for this purpose sur- 

 rounded by a layer of powdered quartz or other 

 suitable material ; and (3) that the furnace 

 is designed for and worked at the lowest voltage 

 convenient. 



In deciding upon the amount of lagging neces- 

 sary, the purpose for which the furnace is to be 

 employed must be considered. The provision of 



