262 PHYSICS. 



with tlie terminals. With reference to the lieating effect of molecular 

 bombardment, a plate of German glass was held in the focus and soon 

 became red hot. Gas then appeared in the tube, which gave the hydro- 

 gen spectrum. This was pumped out and the exi)eriment repeated. 

 The glass could bo heated to dull redness without evolution of gas, but 

 when the heat approached the fusing point, the lines appeared. This 

 hydrogen the author thinks comes from vapor of water which is obsti- 

 nately held in the superficial pores, and which is not entirely driven off 

 by anything short of actual fusion of the glass. From an experiment 

 in which a hole in a mica disk was placed in front of a negative elec- 

 trode of platiiuTm, and the tube opposite the hole was not more darkened 

 than the surrounding portions, Crookes infers that the molecular stream 

 does not consist of particles of the negative pole shot off" from it. With 

 regard to the production of phosphorescence by impact in crystals, the 

 conclusion is arrived at that the rays whose direction of vibration cor- 

 responds to the direction of maximum optical elasticity in the crystal 

 are always originated where any light is given out. — {Nature, xxii, 101, 

 125, June, 1880.) 



More recently, Crookes has written a letter to the secretary of the 

 Eoyal Society, in answer to a challenge from De la Rue, defining his 

 position in reference to the ultra-gaseous or fourth state of matter. 

 This letter concludes thus : " The molecule — intangible, invisible, and 

 hard to be conceived — is the only true matter, and that which we call 

 matter is nothing more than the effect upon our senses of the move- 

 ments of molecules, or, as John Stuart Mill expresses it, ' a permanent 

 possibility of sensation.' The space covered by the motion of molecules 

 has no more right to be called matter than the air traversed by a rifle 

 bullet can be called lead. From this point of view, then, matter is but 

 a mode of motion ; at the absolute zero of temperature the inter-molec- 

 ular movement would stop, and although something retaining the prop- 

 erties of inertia and weight woiild remain, matter, as we know it, would 

 cease to exist." — {Froc. Roy. iSoc, June, 1880; Nature, xxii, 153, June, 

 1880.) 



Marangoni has studied the diathermanous power of liquid films, using 

 for this purpose soapy water. A series of equidistant films 8 or 10 in 

 number was produced in a wide glass tube, and heat rays from a smoked 

 plate at 400^ were reflected through the tube by a mirror, a second 

 mirror at the other end directing them on the face of the thermopile. 

 He found, (1) that the first film absorbs more than half the heat, re- 

 ducing the deflections from 38 to 18 divisions ; (2) the successive films 

 produce decrements as theory indicates ; (3) the diminution of intensity 

 depends very little on reflection, but almost wholly on absorption ; (4) 

 the thinner the film the more diathermanous it becomes ; (5) the dia- 

 thermaneity is not sensibly affected by mixing various salts with the 

 solution of soap. — {Nature, xxi, 620, April, 1880.) 



Lecher has made further experiments on the absorbing action of car- 



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