308 
Scientific Intelligence. 
[Oct. 
As our work has already reached its 9th number, we shall he obliged to go hack 
a little ; and if we should admit amongst our novelties some things not so very new, 
yet as the great majority of our subscribers, owing to the heavy charges attend- 
ing in India the acquisition of knowledge, have not the means of keeping their ac- 
quirements up to the level of modern improvements, we are persuaded they will 
not object to this partial retrospect, especially as it shall only include subjects of 
real interest or importance ; and even those more fortunately situated with regard 
to the facilities of receiving supplies of books may not object to have their memo- 
ries refreshed. 
1. — Novelties in Science. 
1 , — 3/r. Tredgolds new Theory of the Resistance of Fluids* 
Those of our readers who are acquainted with the value of the several theories as 
yet proposed on this subject, will be interested to hear that Mr. Tredgold has pro- 
posed a new one, which as far as we can judge, certainly appears to agree better with 
experiment than that generally received at present. The importance of the subject 
maybe in some degree estimated from the fact of the French Academy of Sciences, 
hating offered a premium for the best series of experiments on the resistance of 
fluids. We shall endeavour to give a concise, but we hope, intelligible account of 
Mr. Tredgold's theory. 
The resistance of fluids, l^Ir. T. divides into three parts, 1. The displacement of the 
fluid before the body can occupy its place, (direct resistance ;) 2. The re-establish- 
ment of the v fluid in the vacancy left by the body ; (minus pressure of the fluid;) 
and 3. Friction. 
The direct resistance of water, as measured by the height ofa column, Mr. T. iinds 
is equal to- 
/ v 3 Sin* 3 d 
v, being the difference between the velocity of the fluid 
and that of the body ; a, the angle which the surface of resistance makes with the di- 
rection of the motion; and g, the space described in a second by the velocity 
due to the force of gravity in vacuo = 32$ feet. The minus pressure, he finds ex- 
pressed by the formula *-■ .• c, being the angle the retiring surface makes 
with the direction of motion ; and v, and g, as before. The combination of these two 
(2 Sin.' 2 a 4 . Sin. 3 c ) for the value of the resistance exclu- 
expressions gives 
4 g 
sive of friction. When the body is a cube, or a cylinder, with the ends per- 
pendicular to the direction of the motion, the angles being 90° the above becomes 
3 v * 
4 
The friction he finds to consist of two parts ; that due to the body, and that due to 
the particles of the fluid itself. The first he supposes to be directly as the square 
of the velocity, and as the surface; in which case/ being put to signify the height ot 
a column equal to the friction on one foot surface, moving with a velocity of one 
foot per second, this will become, when distributed over the whole section s of the 
moving body — and putting Ip = the surface ofthe friction, the expression will be- 
come fjjil— Tile friction of the fluid itself, he considers as affecting the value of 
l by a quantity A a. A being a coefficient depending on the nature of the fluid ; the 
whole friction will then assume the form — *— and consequently the 
(2Sin. 3 a+Sin.*c+fr(l+*dv'l Thg SCCOEd 
whole resistance will be t>- 
4 S 
part of the correction for friction may be neglected in the case of water. 
From the first expression lie finds the resistance exclusive of friction on the fol- 
lowing bodies, will he in proportion to tile numbers set opposite them. 
A Cylinder with flat ends, 1> 
A Cylinder with the hind part a hemisphere, 0,833 
A Cylinder with the fore part a hemisphere, 0,600 
A Sphere, 0,433 
