778 PHILOSOPHICAL TRANSACTIONS. £ANNO 1800. 



or say 1000, to 606, must occasion a deficiency of 579 ra ys of heat. But, by 

 our table, this glass stops only 489 °f tnem '* an ^ tnere will thus be 90 rays of 

 heat left unaccounted for. To enhance the difficulty, this glass, by our 164th 

 experiment, stops also ± of the supposed 394 invisible rays, which will amount to 

 an additional sum of 98. And our 111th experiment shows, that actually a great 

 number of these rays, that otherwise cannot be accounted for, come from the 

 store of heat, the rays of which are of the refrangibility of red light. 



A dark- blue glass stops 801 rays of light ; these, if light and heat were occa- 

 sioned by the same rays, would produce a stoppage of 485 rays of heat ; but we 

 find that our glass stops no more than 362, so that 123 rays cannot be accounted 

 for by this hypothesis. To this we should add 66 invisible rays, that is, 394 X 

 .167, which, according to our 160th experiment, this glass also intercepts. But 

 the 107th experiment, if we reject the hypothesis, immediately explains the 

 difficulty ; for here we plainly see, that only 7 1 rays of heat of the refrangibility 

 of red light are stopped, whatever may be the stoppage of that light itself. A 

 yellow glass stops 819 rays of light : these will occasion a stoppage of 496 rays of 

 heat; but this glass intercepts only 333, and therefore l63 rays of heat must also 

 remain unaccounted for. And, turning to the 1 55th experiment, we find that 79 rays, 

 or -f of the 394 allowed to be invisible ones, are also to be added to that number. 



If in the results of our 2d table we have had an excess of heat, which the last 

 hypothesis would not account for, we shall, on the contrary, meet with a con- 

 siderable deficiency, when we come to consider those of the 3d table. For 

 instance, our tube filled with well-water, including the glasses at the end, inter- 

 cepted 211 rays of light. These, at the rate of 606 to the thousand, would 

 produce only a stoppage of 128 rays of heat; but here we find no less than 558 

 of them intercepted. To evade the pressure of these consequences, it may be 

 said, " that as before every invisible ray was supposed to have been transmitted 

 through glasses, so they may now be all intercepted by liquids." And granting 

 this also to be possible, though by no means probable, for the great extent of 

 these researches has not allowed sufficient time for many experiments to be made 

 that have been planned for execution; yet even then 128 visible and 394 invisible 

 rays to be intercepted, will only make up 522 ; so that a deficiency of 36 must 

 still remain. In sea-water, the balance will stand thus : 288 rays of light give 

 175 rays of heat ; these and 394 invisible rays make up 569 ; but the rays actually 

 intercepted were 682, which argues a deficiency of no less than 1 13 rays. 



But if I have for a moment admitted the entire stoppage of the invisible rays 

 of heat in liquids, the same indulgence cannot be granted for the empty tube, as 

 we know it does neither take place in glasses, nor in air. Therefore we must 

 calculate thus : this compound of glass and air stops 204 rays of light ; these 

 can amount only to 124 rays of heat; but it is found to stop 542 of them, so 

 that 418 remain to be accounted for. Now, we certainly can not suppose more 

 than 100 of them to owe their deficiency to the store of invisible heat; so that 

 318 will still remain unaccounted for. And thus, from the 2d table, we have 



