8i4 



NATURE 



[June 24, 1922 



the immediate ill effects of blocking of the prothoracic 

 spiracles by Tarsonemus woodi, the causal parasite of 

 Isle-of- Wight (Acarine) disease. 



Spiracular muscles (apparently similar in function 

 to those of Apis mellifica) have been found in Vespa 

 sp., Bombus sp., and a wild bee (? Prosopis). In a 

 modified form, they are present in Formica sp., being 

 there apparently attached to the anterior edge of the 

 tergum, and not to the sternal apophysis. 



To see these, as well as the other abdominal muscles 

 of the bee, I may mention that material preserved in 

 equal parts of methylated spirit and formalin, deeply 

 coloured with light green so as to stain the muscles, 

 is excellent. Dissect in water. 



Annie D. Betts. 



Hill House, Camberley, Surrey. 



Symbiotic Bacteria and Phosphorescence. 



In Prof. Gamble's review of Buchner's " Tier 

 und Pfianze in intrazellularer Symbiose" (Nature, 

 May 6) reference is made to the work of Pierantoni, 

 according to whom the luminous organs of cephalopods 

 are " essentially cultures of bacteria in media suitable 

 for their nutrition and in situations favourable for 

 obtaining oxygen." 



The claims which are made for the existence of 

 similar symbiotes in fire-flies and many other phos- 

 phorescent organisms may be extravagant, but Newton 

 Harvey's recent announcement in the Year-book 

 (No. 20 (1921), pp. 196-97) of the Carnegie Institution 

 of Washington is exceedingly important in this con- 

 nection. Harvey worked on two fishes with very 

 large luminous organs — Photoblepharon and Anoma- 

 lops — at Banda in the Dutch East Indies. He found 

 bacteria always present in the organs, and emulsions 

 of these organs behaved exactly like emulsions of 

 luminous bacteria. The light continues night and 

 day without ceasing, independently of stimulation. 

 This is characteristic of the light due to luminous 

 bacteria and fungi alone among organisms. Harvey 

 did not succeed in growing the bacteria artificially, 

 however ; but considering the conditions under which 

 they apparently live, this would, naturally, be a task 

 of great difficulty. Dahlgren (see the same reference) 

 seems to have confirmed Harvey's discovery in other 

 fishes. 



Luciferin and luciferase could not be demon- 

 strated, which is also characteristic of luminous 

 bacteria. F. A. Potts. 



Trinity Hall, Cambridge. 



Stone Preservation. 



May I throw out a suggestion, which, I believe, is 

 new, as to a method for preserving decaying sand- 

 stones from further decay ? 



Certain compounds of alcohol-radicles with silica, 

 when exposed to moist air, hydrolyse, deposit hydrated 

 silica in a coherent form, and thus act as a cement. 

 The ether can be thinned with alcohol, and is a very 

 stable body so long as it is not exposed to moisture, 

 and if a piece of rotten sandstone is treated with 

 it, in the course of a few days the sandstone hardens 

 up and the resulting cement resists the attacks of 

 acids. 



Unfortunately, this process does not solve equally 

 well the important problem of preserving limestones, 

 since, though it binds the particles of limestones 

 together, it does not protect the particles themselves 

 from attack. A. P. Laurie.. 



Heriot-Watt College, Edinburgh, May 31. 



NO. 2747, VOL. 109] 



Oscillation Circuits for the Determination of 

 Di-electric Constants at Radio Frequencies. 



During the last year or so a number of investigators 

 have made use of the underlying principles of the 

 heterodyne system of wireless telegraphy in the de- 

 termination of di-electric constants. The extreme 

 sensitivity of this method, and its freedom from some 

 of the weaknesses which have rendered precise 

 measurements by the older methods difficult of 

 attainment, are rapidly increasing its popularity, and 

 any changes which make for simplicity and for still 

 greater certainty are of interest. 



For no apparent reason circuits of the type used 

 only for receiving signals have, so far as the writer 

 is aware, been employed, though greater efficiency is 

 to be expected from the use of a transmitting circuit 

 in conjunction with such a receiving circuit generating 

 local oscillations. In either case it is preferable 

 that the oscillation circuit, of which the condenser 

 containing the material under investigation forms a 

 part, should not rectify, as rectification is necessarily 

 accompanied by distortion of wave form. 



Instead of using the two electrically insulated cir- 

 cuits hitherto employed the writer prefers that 

 shown in Fig. i, in which simple transmitting and 

 receiving circuits are combined in such a way that 



oscillations of two different frequencies can"' be 

 generated although both valves are fed from the 

 same filament-heating and anode batteries. An 

 additional reason why only one valve should be used 

 for rectification with this particular arrangement lies 

 in the fact that, if both valves were rectifying, the 

 unidirectional pulses of current of audible frequency 

 produced in each of the circuits by the rectification 

 of the interfering oscillations would tend to produce 

 a steady current, since they would be quite out of 

 phase with each other. 



As is well known to workers who have had experi- 

 ence of apparatus of this kind, changes in the value 

 of the filament-heating current by altering what is 

 virtually the resistance of a valve affect, to a certain 

 extent, the frequency of the oscillations generated. 

 This trouble can be lessened to a very great extent 

 by taking the heating current for both filaments 

 from the same battery of accumulators. The fila- 

 ments can be connected in parallel, but there is more 

 to be gained by connecting them in series, as will be 

 apparent from the figure. It will be seen that, 

 although the two grids are at the same potential 

 with respect to earth, their potentials with respect 

 to the heated filaments are quite different ; in the 

 case of the valve shown in the lower half of the 

 figure the potential difference is such that it can 

 " oscillate " only, while the other valve can both 

 oscillate and rectify. 



In conclusion, it should be stated that this letter 

 is written with the kind permission of the Director 

 of Artillery, War Office. P. A. Cooper. 



Explosives Branch, Research Dept., 

 Woolwich, April 15, 1922. 



