4-4-4 Prof. E. Wartmann's Seventh Memoir on Induction : 



duced and persists for a long time. If the wick of the lamp 

 is lowered a little, the drop is seen to rise centrally and give 

 passage to a large bubble of vapour, which is immediately 

 followed by several others. Each of these bubbles is unique 

 in the mass. The form of the liquid is no longer stellate, but 

 elongated. The drop turns as around a vertical axis, passing 

 through one of the focuses of the ellipsoid. A further decrease 

 of temperature sometimes causes the cessation of this gyratory 

 motion ; then the drop presents itself as a beautiful biconvex 

 lens, which, by its immobility and its perfect transparency, 

 most completely resembles an object-glass. 



198. This remarkable form suggested to me the idea of 

 submitting to a decisive and new proof a question still contro- 

 verted. The question has been often asked, whether the 

 caloric which reaches the drop traverses it by radiation without 

 raising its temperature, or whether it is reflected by it. In 

 the first case, the refraction in the centre of the lens must 

 produce a focus at which the temperature will be certainly 

 superior to that of the neighbouring points. In the second, 

 this lens will form a circular screen, behind which the tempe- 

 rature will be lower than in the space submitted to the direct 

 radiations of the capsule. To decide between these alterna- 

 tives, I operated with small thermometers open at the top and 

 furnished with a small ivory scale with arbitrary graduations. 

 The stem passes through a thick cork disc fixed into the hol- 

 low of a glass funnel, so that their bulb makes a slight projec- 

 tion a-t the extremity of the beak. The instrument thus 

 clothed, and placed above a drop m, 028 in breadth, demon- 

 strates that the latter is not the seat of any refraction. Not 

 only is there no calorific focus, but the temperature increases 

 in proportion as the thermometer is raised above it, on account 

 of the radiation caused by the parts of the metal which are 

 not concealed by the liquid. This radiation explains why the 

 heat near the surface of the lens is much higher than in its 

 interior. 



199. The influence of a musical sound suitably chosen on 

 the constitution of a fluid vein is well known : that influence is 

 explained by the periodicity of the variations which are esta- 

 blished in the diameter of the vein at its origin. A body in 

 the spheroidal state is often exposed to regular and periodical 

 movements, which give to it in particular a stellate form. 

 Numerous experiments have proved to me that this form is 

 not at all changed by the sonorous pulsations of a diapason 

 communicating with the support of the capsule, although those 

 pulsations be energetic enough to derange and alter the posi- 

 tion of the capsule. 



