Intelligence and Miscellaneous Articles. 319 



which seems to give results agreeing with those of ordinary- 

 methods. 



It would be interesting to extend this research to different gases 

 and at various pressures. The method started enables us to inves- 

 tigate the electrical effects of radiation under conditions which are 

 much simpler, and more accessible to measurement, than in the 

 experiments of the authors cited above*. 



The effect of the voltaic arc is enormously increased by intro- 

 ducing certain metals ; among those which I have tried, aluminium 

 is the most effective ; then come zinc and lead. These, I think, 

 are the metals of which the ultra-violet spectrum is richest ; it is 

 also to be observed that they are the most positive metals in Yolta's 

 series. 



I have made some experiments by another method. Having 

 charged my gauze condenser by a battery, I leave it insulated under 

 the action of the rays for some time, and I then measure the 

 discharge- current. In order to increase the charge and retard the 

 loss due to the rays, a large and known capacity (standard mica 

 condenser) is joined to the illuminated condenser. In this way the 

 resistance of the layer of air may be calculated ; the results are in 

 agreement with those obtained by the first method. If the disks 

 are of different metals, the effect of the rays tends to equalize their 

 potentials ; and by connecting the two armatures by the galvano- 

 meter, after a sufficient time a charge-current is obtained corre- 

 sponding to the electrical difference of the metals. — Comptes Rendus, 

 April 16, 1888. 



INVESTIGATIONS ON THE INFLUENCE OF MOISTURE ON THE 

 LENGTH OF CERTAIN WOODS, AND IVORY. BY RUDOLFF 

 HILDEBRAND. 



The results of this research are summed up by the author as 

 follows : — 



(1) Within certain limits, the length of woods in the direction 

 of their fibres depends on the proportions of water in the cell-wall, 

 and with an absorption of water amounting to 20-30 per cent, the 

 increase of length may amount to 0*1 to 2 per cent., according to 

 the kind of wood. 



(2) The woods are shortest when all water is withdrawn from 

 them. 



(3) Dry woods are highly hygroscopic. 



(4) Woods attain their greatest length by absorbing water from 

 air charged with it, or by complete soaking with water. 



* This Note was written before I knew of a recent research of M. 

 Arrhenius (Wiedemann's Annalen, No. 4, 1888), who obtains analogous 

 results by working either with phosphorescent air, which forms part of an 

 electrical discharge-tube, or with rarefied air illuminated from the outside. 

 The method of M. Arrhenius is not delicate enough for pressures above 

 20 millim., and it does not bring out the difference in the function between 

 the two electrodes of the current in air. 



Compare also Phil. Mag. [5] vol. xxv. p. 314 (Ed. Phil. Mag.). 



