POPULAR MISCELLANY. 



571 



trees are fifteen feet in diameter and live to 

 a great age. A group of trees in the prov- 

 ince of Toosa, about a century old, are esti- 

 mated to be equivalent to about forty thou- 

 sand pounds of crude camphor. The cam- 

 phor is extracted from chips taken from the 

 roots or from the stem near the root, the 

 wood yielding about five per cent of cam- 

 phor, and the root a larger proportion. The 

 annual export of Japan camphor averages 

 about five million pounds. The forests in 

 Japan owned by the people are now almost 

 denuded of timber, but the Government still 

 possesses large woods of camphor trees, 

 which, it is estimated, will maintain a full 

 average supply of the gum for the next 

 twenty-five years. Plantations of young 

 trees are also making and well taken care 

 of ; and although camphor has not hitherto 

 been extracted from trees less than seventy 

 or eighty years old, it is expected that under 

 the present intelligent management equally 

 good results may be realized in twentj'-five 

 or thirty years. The Japanese Department 

 of Forests, which has the control of these 

 woods, is under good management. 



Constitntion of tbe Ether. Assuming 

 that the elastic solid theory of the ether has 

 failed, Mr. R. T. Glazebrook thinks that the 

 properties of the ether which would lead to 

 the equations that represent the laws of the 

 transmission of light, may be found in the 

 labile ether of Lord Kelvin. This is an elastic 

 solid, or quasi solid incapable of transmitting 

 normal waves. Such a medium would col- 

 lapse unless of infinite extent, or else fixed 

 at its boundaries. A soap bubble affords in 

 two dimensions an illustration of it, the ten- 

 sion being independent of its dimensions. 

 "Waves of displacement parallel to the sur- 

 face of the film would not be transmitted. 

 But such a film in consequence of its ten- 

 sion has an apparent rigidity for displace- 

 ments normal to its surface ; it can transmit 

 transverse waves with a velocity which de- 

 pends on the tension. Now the labile ether 

 is a medium which has, in three dimensions, 

 characteristics resembling those of the two 

 dimensional film. Given such a medium 

 and there is nothing impossible in its concep- 

 tion and the main phenomena of light fol- 

 low as a necessary consequence. Lord Kel- 

 vin, again, has shown us how such a medium 



might be made up of molecules, having rota- 

 tion in such a way that it could not be dis- 

 tinguished from an ordinary fluid in respect 

 to any rotational motion ; it would, how- 

 ever, resist rotational movements with a 

 force proportional to the twist, just the force 

 required. The medium has no real rigidity, 

 but only a quasi rigidity conferred on it by 

 its rotational motion. The actual periodic 

 displacements of such a medium may consti- 

 tute light. We may claim, then, with some 

 confidence, to have a mechanical theory of 

 light. But nowadays the ether has other 

 functions to perform, and there is another 

 theory to consider, which at present holds 

 the field. Maxwell's equations of the elec- 

 tro-magnetic field are practically identical 

 with those of the quasi-\ab\\e ether. The 

 symbols which oocur can have an electro- 

 magnetic meaning ; we speak of permeability 

 and inductive capacity instead of rigidity and 

 density, and take as our variables the electric 

 or magnetic displacements instead of the 

 actual displacement of the rotation. Still, 

 such a thing is not mechanical, and we have 

 no satisfactory mechanical theory of the 

 electro-magnetic field. But the theory of 

 the quasi-X-AhWc ether may be applied, and 

 gives two analogies according as we regard 

 the density of the medium to be analogous 

 to electrostatic inductive capacity or to mag- 

 netic permeability. 



Explorations iu Thibet. In a paper on 

 Recent Explorations in Thibet, Mr. E. Del- 

 mar Morgan said in the British Association 

 that the discoveries made by travelers, begin- 

 ning with the Schlagintweit brothers and 

 ending with Dr. Thorold's recent journey, 

 had opened out new fields of research in 

 hitherto inaccessible parts. They had deter- 

 mined the continuity of the Kuen Luen 

 mountain system through twenty degrees of 

 longitude, and made known the direction 

 and structure of the principal chains. They 

 had shown the lacustrine character of the 

 central plateaus, and traced almost to their 

 sources some of the mightiest rivers of Asia. 

 They had thrown light on the climatic con- 

 ditions of these lofty deserts, and seen an 

 abundance of animal life on them. Their 

 researches had proved the existence, in for- 

 mer times, of a line of flourishing oases 

 along the northern foot of the Kuen Luen, 



