NEW THEORY OF TIDES BY CLARK. 
609 
A stove made of earthenware, and placed on 
one side of the partition, contains all the fuel 
required, and the hotair circulates round and 
round the partition before it is eventually car- 
ried off by the small tubular chimney. An 
extensive surface of 32 square feet is thus 
presented to the air at a moderate elevation 
of temperature, about 212 ; and, accordingly, 
scarcely any thing passes up the chimney 
which has not been almost entirely exhausted 
of its heat. This stove saves equally time, 
trouble, and fuel, and is quite free from the 
dust of a common fire. 
DR. REID’S SYSTEM OF VENTILA- 
TION. 
At the conclusion of the same meeting, 
the Society adjourned to a new apartment, 
constructed by Dr. Reid, illustrative of his 
arrangements for* ventilation, &c. It is 32 
feet long, and 18 broad, the floor being pierc- 
ed with 50,000 apertures for the admission 
of air. A series of experiments have since 
been commenced in it, in one of which, in- 
tended to show the working of the flues, lOO 
individuals remained in it for upwards of an 
hour, the room having been alternately fi^ed 
with warm and cold air, and partially charged 
with ether and nitrous oxide, at different 
times. The air was completely renewed by 
a slow and insensible current every five 
minutes, and the various changes so gradually 
induced, that it was impossible to tell when 
they commenced. The plan is equally appli- 
cable to public buildings and private dwell- 
ing-houses, as well as to hospitals, churches, 
public assemblies, and all tho<e places where, 
from a crowded apartment, the air becomes 
oppressive both from heat and noxious 
effluvia. — Scotsman. 
A NEW THEORY OF THE TIDES, 
by ALEX. CLARK, ESa. ENGINEER. 
For the purpose of literal demonstration, 
let us suppose that the distance of the 
earth’s centre from the centre of the moon 
is 240,000 miles, that the diameter of the 
earth is 8000, and that of the moon 2000 
miles, and that they are dense in propor- 
tion to their sizes. Then as globes are to 
each other as the cubes of their diameters, 
the density of the earth will be sixty-four 
times that of the moon, and the centre of 
gravity of both sixty-four times nearer the 
former than the latter. This pointy is 
within the body of the earth, or about 3/o0 
miles from its centre. The moon is said to 
revolve round the earth, in which saying 
there seems no impropriety; but for our 
purpose it is necessary to state that, strictly 
speaking, these two bodies revolve on the 
above point, which is the centre of gravity 
both combined. The above numbers are 
not correct, but they are sufficient for our 
purpose. 
The centrifugal force, created by the 
revolution of the earth in this small orbit 
round the combined centre of gravity of the 
earth and moon, will have a constant 
tendency to make the earth fly off from 
that centre, which she would do if it were 
uot for the attraction of the moon acting 
with equal force in a contrary direction. The 
earth is therefore between two forces, and 
being partly fluid, the fluid parts are elong- 
ated in the direction of these forces. This 
elongation constitutes the double diurnal 
lunar tide, which flows in a contrary direc- 
tion to the diurnal motion of the earth on 
its axis, Now for the solar tides. 
According to the law of universal gravi- 
tation, every particle of matter of the ter- 
restrial globe will attract every particle of 
matter in the lunar globe, and vice versa. 
The attraction between those bodies may be 
compared to a chain binding them together, 
every link of which sustains the same strain, 
for a chain freely suspended between two 
points cannot have a greater strain at one 
part than another (barring weight, which in 
this case it is supposed to be devoid of). The 
attraction at the moon must therefore be 
exactly equal to that at the earth, and as 
the centripetal and centrifugal forces are 
always equal and contrary, they must 
produce results on the moon’s surface similar 
to the terrestrial tides, provided that lumi- 
nary be surrounded with fluids like the earth. 
Apply this doctrine to the earth as influenced 
by the sun, and the effect must be a double 
diurnal solar tide on the earth. 
The spring tides are caused by the central 
forces acting parallel and in unison at the 
fulls and changes of the moon, and the neap 
tides by acting at right angles or in opposi- 
tion to each other at the quarters. 
From what I have said it might be sup - 
posed we have four diurnal tides, viz. two 
solar and two lunar ; but this is not the 
case, the sun’s influence being much smaller 
than that of the moon, perhaps in the pro- 
portion of 1 to 5. The solar tide combin- 
ing with the lunar, becomes evanescent, and 
will be best shown by figures as follows ; — 
Supposing the lunar tide at any particular 
place to rise 15 feet, and that at the same 
place the solar tide rises 3 feet, then when the 
moon is at the full or change, and her attrac- 
tion acts in conjunction with the sun’s, we 
shall have 15 3=18 feet, or a springtide ; 
but when the moon is at the quarters and acts 
in opposition to the sun, we shall have 15 — 3 
= 12, or a neap tide. — Mechanic's Magazine, 
