Radiation of Heat by Gaseous Matter, 275 



taken up by the former is greater than that taken up by the 

 latter. The difference, however, may really be due to the me- 

 chanical carrying away of a portion of the chloride by the current 

 of air. 



On the 13th of September these experiments were resumed. 

 The dry air then gave a deflection of less than 2 degrees ; the 

 air direct from the laboratory caused, in one experiment, the 

 needle to move from 20 degrees on one side of zero to 28 on the 



o 



other. In a second experiment the undried air caused the needle 

 to move from 18° on one side of zero to 32° on the other. 



Experiments made on the 17th entirely corroborated this 

 result. Three successive trials made the action of the undried 

 air of the laboratory 29°, 31°, and 30° respectively, the deflec- 

 tion produced by the dried air being less than a single degree. 

 On this day, therefore, the action of the aqueous vapour of the 

 air was at least thirty times that of the air itself. 



Almost every week-day during the last four months, experi- 

 ments similar to the above have been executed, and in no case 

 have I observed a deviation from the result that the absorptive 

 action of the aqueous vapour of the air is quite enormous in com- 

 parison with that of the air itself. Further on I will give an 

 array of figures illustrating this point. 



As I became more and more master of my apparatus, and 

 more acquainted with the precautions necessary in delicate cases, 

 the absorption of air and the elementary gases diminished more 

 and more. I was induced to abandon the use of pumice-stone 

 as well as of chloride of calcium, and to construct my drying- 

 apparatus in the following way. The internal portion of a mas- 

 sive block of pure glass was pounded to small fragments in a 

 mortar; these were boiled in pure nitric acid, and afterwards 

 washed several times with distilled water so as to remove all 

 trace of the acid. They were then dried, afterwards moistened 

 with pure sulphuric acid, and introduced by means of a funnel 

 into a U-tube. The funnel was necessary to preserve the neck 

 of the tube from all contact with the acid, the least action of 

 which upon the corks used to close the tube was sufficient to 

 entirely vitiate the experiments. At the top of each arm of the 

 U-tube a quantity of dry fragments of glass was placed, so that 

 if any dust or particles from the cork or sealing-wax chanced to 

 reach the interior they fell upon the dry glass. 



Similar precautions were taken with the caustic-potash tube. 

 Pure white marble was pounded to fragments and subjected to 

 the action of a dilute acid, which removed the outer surface of 

 the fragments. These were afterwards washed in distilled water 

 and dried, then moistened with pure caustic potash, and intro- 

 duced into the U-tube in the manner already described. It was 



