On Caloric Radiation. 301 
Paris. In spite of these obstacles, and notwithstanding the few 
observations which could be collected, M. Nicollet has already 
‘calculated the parabolic orbits, some particularities of which are 
sufficiently remarkable. The first comet passed its perihelion 
Feb. 26, 1818. ‘Its inclination varied little from 90°; it is the 
greatest which has been yet observed. The second did not reach 
its perihelion till the 24th January 1819. It presented at first 
some resemblance to the comet of 1805.. The third was at its 
perihelion on the 5th December 1818, and on the 13th of the 
same month its distance from the earth was only twelve hundredth 
parts of the distance of the sun. This last comet is retrograded ; 
the two others ae direct. 
LII. Intelligence’ and Miscellaneous Articles. 
POSTSCRIPT TO MR. MEIKLE’S PAPER ON CALORIFIC RADIA- 
TION. 
To Mr. Tilloch. 
Six, — In perusing my paper in your last number, I find I have 
inadvertently made a mistake in accusing the epicycloidal teeth 
of tapering suddenly. In so doing, I meant that kind of teeth 
which have the form of the involutes of the circles beyond which 
they project. These, there can be no doubt, have an enormous 
friction. When a certain force applied perpendicularly to the 
fadius of a wheel, is just sufficient to turn it round, it is clear, 
that if the force act in any other direction, the pressure on the 
teeth must be augmented in the ratio of radius to the cosecant 
of the angle which the direction of this pressure makes with the 
radius of the wheel ; and of course, the friction not only on the 
teeth, but likewise at the centre of each wheel, must be augment- 
ed in the same ratio. 
By glancing at Mr. Renhie’s experinients, I am disposed to 
apree with Mr. Tredgold—that most experimentalists have been 
rather remiss in hot carefully measuring the degree of flexure. 
en a bar ‘resting loosely on two props becomes bent by the ac- 
‘tion of a weight on its middle, the strain will be increased in the 
ratio of radius to the secant of the angle which the bar makes 
with the horizon at the point where it rests on the prop. But the 
‘artn of the lever, between the weight and prop, will also be 
lengthened. Allowance for these should therefore be made, be- 
fore any conclusion can be drawn with accyracy. 
This seems to be the reason of what Buffon has remarked ih 
‘his experiments—that in beams differing only in length, the va- 
riation of strength did not exactly follow the inverse ratio of the 
Tengths ; the real strengths seeming to fall ‘a little short of the 
computed ; 
