320 Intelligence and Miscellaneous Articles. 



(5) The length of the woods increases, from the condition of 

 dryness, with the moisture. After the wood has attained the 

 greatest length the absorption of water from moist air continues, 

 but more slowly than before. 



(6) Certain kinds of wood, after being completely dried, are 

 unable to attain the length which they have when air-dried. The 

 behaviour of plum-tree wood is very remarkable : after reaching a 

 certain maximum, which is inversely proportional to the increase 

 of moisture, its length decreases. 



(7) The length and weight of the woods increase with the rela- 

 tive moisture of the air, and decrease with it. 



(8) The usual modes of treatment of wood — polishing, soaking 

 with oil — do not cut off the influence of saturated air. The best 

 is varnishing. 



(9) In the longitudinal direction of the teeth, ivory is liable to 

 great changes in length as the moisture varies. — Wiedemann's 

 Annalen, No. 6, 1888. 



LECTURE-EXPERIMENT. BY M. P. SIMON. 



There are a certain number of experiments which serve to de- 

 monstrate the fact that, when a body is heated, the rays which it 

 emits are a function of the temperature, that they follow each other, 

 superposing themselves in the order of the colours of the spectrum 

 from red to violet. 



A known method consists in stretching a platinum wire in the 

 flame of a Bunsen-burner and in viewing it with a prism. The 

 spectrum is then seen complete in the centre and diminishing 

 towards the edges, where it only contains red rays. 



I have arranged the experiment in a different manner, which 

 produces the phenomenon very brilliantly. A spectroscope is taken, 

 and turned towards an ordinary gas-jet so as to obtain a spectrum ; 

 then across the slit, and very near it, a platinum wire is stretched 

 which is made incandescent by a current, a rheostat being interposed 

 in the circuit. In these conditions, and without heating the wire, 

 the spectrum is traversed by a dark line. The current is now gra- 

 dually passed through the wire. At a given moment the dark line 

 will disappear in the red only. Evidently the wire emits a red 

 radiation of the same intensity as that of the spectrum. 



The experiment is continued by gradually increasing the intensity 

 of the current. We see the wire stand out brightly in the red of 

 the spectum, while it becomes invisible in the green, and is obscure 

 in the violet. Gradually heating, the invisible part gradually ex- 

 tends towards the violet, until the entire line stands out brightly 

 over all the spectrum. This experiment is very easily made by 

 regulating suitably the distance of the source of light from the 

 spectroscope, that is to say, regulating the intensity of the spec- 

 trum. — Journal de Physique, February 1888. 



