neighbourhood of strongly Illuminated Bodies. 217 



the box tobacco smoke could be readily blown in, or ammonic- 

 chloride smoke by a current of air directed into the box 

 through a heated tube containing ammonic chloride. The 

 body under examination was supported near the glass end of 

 the box either by means of the small adjustable clip shown in 

 fig. 7, or passed through the cork in the opposite wooden end 

 of the chamber. Fig. 6 illustrates this mode of support the 

 thin line representing a fine platinum wire attached to two 

 stout copper wires through which a current to ignite the wire 

 could be passed. Metal rods thus supported could be directly 

 heated from without by means of a gas-flame, and, if desired, 

 be insulated b} passing through glass tubes in the cork. 



Ordinarily the convergent beam of the electric light heated 

 the body sufficiently, especially when it had been previously 

 blackened in the smoke of burning camphor. For the exa- 

 mination in dry air and in different gases, either at the atmo- 

 spheric or at lower pressures, the more complicated apparatus 

 shown in fig. 8 has been employed. The larger end of the 

 horizontal observing vessel is closed with a plane glass plate, 

 through which observations were made. The other end of the 

 vessel was closed with an india-rubber cork carrying two 

 thermometers. The one served to indicate the temperature of 

 the air within the vessel; the cylindrical bulb of the other 

 was covered with camphor smoke and served as the surface 

 upon which the coat formed, and also indicated its tempe- 

 rature approximately. Inert gases were dried by passing 

 through concentrated sulphuric acid and through asbestos 

 mixed with phosphoric anhydride; others, like ammonia, by 

 passing through finely divided calcic oxide and caustic potash. 

 The gases then passed through a wide tube containing am- 

 monic chloride into the experimental chamber. By applying 

 a gentle heat to this tube of ammonic chloride, the gas could 

 readily be charged with its particles. For pressure in excess 

 of the atmospheric, the form of apparatus show T n in fig. 9 

 has been employed. 



For the examination in liquids the box shown in fig. 10 

 was constructed. It has two plain glass sides. The double 

 brass tube w T as about 0'5 centim. in diameter, and passed 

 through a cork in the back of the box: this tube was heated 

 either by a current of steam or by simply converging the 

 beam from the lamp upon it. To render the liquid turbid, 

 particles of dried ferric oxide have been found to answer well. 

 With this form of apparatus, as also with those previously 

 described, the light has been passed in through the side of the 

 vessel, the body being examined through the glass in a line with 

 its axis but at right angles to the direction of the beam of light. 



