444 Prof. Tyndall on Calorescence. 



5. The bulb of a pipette : effects striking, but not quite so 

 brilliant as with the less regularly shaped small flasks. 



It follows as a matter of course, that where platinum is raised 

 to whiteness, the combustion of wood, charcoal, zinc, and mag- 

 nesium may also be effected. 



By the arrangement here described, platinum has been raised 

 to redness at a distance of 22 feet from the source of the rays. 



The best mirror, however, scatters the rays more or less ; and 

 by this scattering, the beam at a great distance from the lamp 

 becomes much enfeebled. The effect in free air is intensified 

 when the beam is caused to pass through a tube polished within, 

 which prevents the lateral waste of radiant heat. Such a tube, 

 placed in front of the camera, is represented at AB, fig. 7, Plate IV. 

 The flask may be held against its end by the hand, or it may be 

 permanently fixed there. With a battery of fifty cells, platinum 

 may be raised to a white heat at the focus of the flask. 



Again, instead of a flask filled with the opake solution, let a 

 glass or rock-salt lens (L, fig. 8), 2*5 inches wide, and having a 

 focal length of 3 inches, be placed in the path of the reflected 

 beam. The rays are converged ; and at their point of convergence 

 all the effects of calorescence and combustion may be obtained. 



In this case the luminous rays are to be cut off by a cell (m n) 

 with plane glass sides ; it may be placed either before or behind 

 the lens. 



Finally, the arrangement shown in fig. 9 may be adopted. 

 The beam reflected by the mirror within the camera is received 

 and converged by a second mirror, x ] y f . At the point of con- 

 vergence, which may be several feet from the camera, all the 

 effects hitherto described may be obtained. The light of the 

 beam may be cut off at any convenient point of its course; but 

 in ordinary cases the experiment is best made by employing the 

 bichloride instead of the bisulphide of carbon, and placing the 

 cell (m n) containing the opake solution close to the camera. 

 The moment the coal-points are ignited, explosion, combustion, 

 or calorescence, as the case may be, occurs at the focus. 



The ordinary lamp and camera of Duboscq may be employed 

 in these experiments. With proper mirrors, which are easily 

 procured, a series of effects which, I venture to affirm, will in- 

 terest everybody who witnesses them, may with the greatest faci- 

 lity be obtained. 



It is also manifest that, save for experiments made in dark- 

 ness, the camera is not necessary. The mirrors and filter may 

 be associated with the naked lamp. 



I have sought to fuse platinum with the invisible rays of the 

 electric light, but hitherto without success. In some experi- 

 ments I have employed a large model of Foucault's lamp, which 



