22 



REPORT — 1841. 



III. We hasten, then, to the third part of our Report. We propose very 

 briefly to reflect on the consequences deducible from the computations we 

 have entered into ; and to conclude by adding a few remarks tending to sug- 

 gest the proper mode of conducting experiments which shall serve a better 

 purpose in eflecting the object of establishing theory. We may observe then, 

 1st, that experiments on the permanent state of temperature at different points 

 of a long bar of a good conducting substance, and which radiates into air, 

 are utterly valueless in this matter. To prove this, we will write down the 

 difference between the calculated and observed values of the temperature for 

 a few cases. 



Exp. I. 



It is altogether impossible to decide which is the best formula from these 

 results. Apparently Formula I. is as good as any of them, and yet we are 

 sure, a priori, that it is absolutely erroneous. The ratios of the error to the 

 whole temperature when greatest are, for the different formulae, 



I. ^49, II. -465, III. ^458, IV. -272. 



These ratios are very considerable, and as they all arise at the point of 

 greatest distance from the heated extremity, they prove clearly enough that 

 the effect due to the presence of the air is far greater than that which arises 

 from the diff'erence of radiation between Newton's law and the law of nature. 

 But even if experiments of this kind were made in a vacuum, it is probable 

 that the law of change would be found to remain so uniform as to admit of 

 its being represented by either of the equations resulting from the second, 

 third, or fourth hypothesis. Nor will our conclusions be more satisfactory 

 on referring to M. Despretz's experiments. Let us write down the errors in 



The maximum ratios of the error to the whole temperature are 



I. ^42, II. -36, III. ^37, IV. -28. 



We must remark again, that this experiment, as contrasted with the fore- 

 going, presents us with most anomalous results. Both were made on a bar 

 of iron ; the temperature of the surrounding air was nearly the same in both ; 

 the extreme temperatures of the former lie beyond those of the latter on each 

 side ; and yet the former verifies, or nearly so, all the formulae, — the latter 

 disproves them all. We trust neither ; nor do we think the difference can be 

 attributed to the coating with which the iron was furnished in the second 

 experiment, although that might produce some effect. We feel, therefore, 



