VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. 647 



provided the breadth of it was small in respect of its distance from the earth; but 

 otherwise will be considerably below the middle. If the breadth of the band was 

 equal to the distance of its lower edge from the earth, the height of the lower 

 edge would be 4 of that above found; and if the breadth was many times greater, 

 would be half of it. 



In the common aurora borealis, an arch is frequently seen low down in the 

 northern part of the sky, forming part of a small circle. What this is owing to, 

 he cannot pretend to say; but it is likely that it proceeds from streams of light 

 which appear more condensed when seen in that direction than in any other, 

 and consequently that the streams which form the arch to an observer in one 

 place, are different from those which form it to one at a distant place, and con- 

 sequently that no conclusion, as to its height, can be drawn from observations of 

 it in different places. Attempts however have been made to determine the height 

 of the aurora from such observations, and even from those of the Corona; 

 though the latter method must surely be perfectly fallacious, and most likely 

 the former is so too. 



XI. Observations on Respiration. By the Rev . J . Priestley , LL.D.j F.R.S. p. 106. 



When Dr. P. wrote the observations on the subject of respiration, published 

 in the Phil. Trans, vol. 66, p. 226, he supposed, that in this animal process there 

 was simply an emission of phlogiston from the lungs. But the result of his late 

 experiments on the mutual transmission of dephlogisticated air and of inflam- 

 mable and nitrous air, through a moist bladder interposed between them, and 

 likewise the opinions and observations of others, soon convincied him, that, be- 

 sides the emission of phlogiston from the blood, dephlogisticated air, or the aci- 

 difying principle of it, is at the same time received into the blood. Still however 

 there remained a doubt how much of the dephlogisticated air which we inhale 

 enters the blood, because part of it is employed in forming the fixed air, which 

 is the produce of respiration, by its uniting with the phlogiston discharged from 

 the blood ; for such he takes it for granted is the origin of that fixed air, since 

 it is formed by the combination of the same principles in other, but exactly simi- 

 lar circumstances. 



Dr. Goodwyn's very ingenious observations prove, that dephlogisticated air is 

 consumed, as he properly terms it, in respiration ; but, for any thing that he has 

 noted, it may be wholly employed in forming the fixed air above-mentioned. He 

 has proved indeed, that the application of dephlogisticated air to the outside of 

 a vein will change the colour of the blood contained in it. But this might have 

 been effected by the simple discharge of phlogiston from the blood, when it had 

 an opportunity of uniting with the dephlogisticated air thus presented to it. He 

 does not however seem to suppose, that there is any phlogiston discharged from 



