VOL. XLIII.] PHILOSOPHICAL TBANSACTIONS. 1]/ 



tubes all over; yet the regressive and rotatory motion was still manifest, with very 

 little, if anv difference; not more dian might be well accounted for, from the in- 

 crease of resistance by wetting. 



These 2 experiments fully convinced him, that neither attraction nor repulsion 

 would be of any assistance in solving the rotation. On considering therefore the 

 matter further, he found nothing was wanting, but that the moving tube should 

 swell towards the fire; and indeed he thought he could perceive such a swelling 

 in Mr. Orme's long tube of 4-l feet, which he saw first placed near a good fire in 

 the manner before described. For, allowing such a swelling, gravity must draw 

 the tube down, when supported near its extremities horizontally ; and a fresh part 

 being exposed to the fire, and swelling out again, must fall down again, and so 

 on successively ; which is, in other words, a rotatory motion towards the fire. 



When the supporting tubes are brought near each other, as well as near the 

 centre of the supported tube, then the parts hanging over on each side, being 

 larger than the part which lies between the supporters, will, by their weight, draw 

 downwards, and consequently force the middle part, resting on its two fulcra, up- 

 wards ; and being less advanced towards the fire, as being less heated, will, by their 

 oblique situation, draw the middle part backward also from the fire : which effects, 

 being successive, will exhibit a rotatory regressive motion, quite contrary to what 

 the tube had when supported near its extremities : and when a single tube lies in- 

 clining opposite to the fire, either to the right-hand or the left, out of a plane 

 perpendicular to the surface of the fire, gravity will not permit the curved part to 

 rest, but draw it down, till it coincides with a plane perpendicular to the horizon ; 

 and consequently as new curves are generated, new motions will be so too; that 

 is, the tube will be made to move about its axis; but with this difference, when 

 the tube inclines to the right-hand, the motion about the axis will be from east to 

 west; when to the left-hand, from west to east. The justness of this reasoning is 

 made manifest with a very little trouble; only bending a wire, and supporting it 

 first near its extremities, then near its centre on each side, afterwards inclining it 

 to the right, and then to the left; the bending in every case representing the 

 curved part of the tube next the fire. And that this solution is the true one, 

 seems ftirther probable from hence, that when 4 supporters were made use of, 

 one at each extremity, and two near the middle, there was no motion at all either 

 backward or forward. Now is it of any service to object here, that the increase 

 of contact hinders the motion? because, on the plane of glass, so large as to have 

 a much greater contact with the tube, both a rotatory and regressive motion was 

 manifest. 



