G A 
depth of water is n'o more than fix luindrcd and tliirty- 
fonr feet, which is not half a quarter of a mile. If, to 
remedy tliis, vve make life of a tube fifty indies lo'no, 
which for (frenpth may be a nu)fleet-barrel, and fiippofe 
the air comprclled into an hundredth part of lialf an inch; 
tlien, as I : 99 : : 400 : 39600 inches, or 3300 feet; even 
tliis is but little more than half a mile, or 2640 feet. But 
fince it is reafonable to fuppofe the cavities of thefea bear 
fome proportion to the molintainous parts of the land, 
Ibme of which are more than three miles above the ean h’s 
furface, therefore, to explore fuch great depths. Dr. 
Hales contrived a new form for his fea-gage, or rather for 
the gage-tube in it, as follows. BCD!' fig. 2. is a hoi. 
low metalline globe, communicating on the top with a 
long tube A B, whofe capacity is a ninth part of that 
globe. On the lower part at D, it has alfo a fliort tube 
1 ) E, to (land in the mercury and treacle. The air con¬ 
tained in the compound gage-tube is compreflTed by the 
water as before ; but the degree of compreflion, or height 
to which the treacle has been forced, cannot there be I'een 
through the tube ; therefore, toanfwerthat end, a flender 
rod of metal or wood, with a knob on the top of the tube 
A B, will receive the mark of the treacle, and (how it 
when taken out. If the tube A B be fifty inches long, 
and of fuch a bore that every inch in length fhould be a 
cubic inch of air, and the contents of the globe and tube 
together five hundred cubic inches; then, when the air 
is comprelled within an hundredth part of the whole, it is 
evident the treacle will not approach nearer than five 
inches of the top of the tube, which will agree to the 
depth of 33QO feet of water as above. Twice this depth 
will comprefs the air into half that fpace nearly, viz. two 
inches and an half, which correfpond to fix thoufand fix 
hundred, which is a mile and a quarter. Again, half 
that fpace, or one inch and a quarter, will fliow double 
the former depth, viz. thirteen thoufand two hundred 
feet, or two miles and an half; which may probably be 
very nearly the greatefl depth of the fea. 
2, The Bucket Sea Gage, This infirument was 
alfo contrived by Dr. Hales, to find the different degrees 
of coolnefs and faltnefs of the fea at different depths. It 
confiftsof a common houfehold pail or bucket made with 
two heads. Thefe heads have each a round hole in the 
middle, about four inches in diameter, covered with 
fquare valves opening upward ; and that they may both 
Open and flint togeiher, there is a fmall iron rod fixed to 
the upper part of the lower valve, and the other end to 
the lower fide of the upper valve : I'o that, as the bucket 
defeends with its finking weight into the fea, both the 
valves may open by the force of the water, which by that 
means has a free paffage through the bucket. But when 
Ihebucket is drawn up, then both the valves (hut by the 
force of the water at the upper part of the bucket; fo 
that the bucket is drawn up full of the loweft fea-water 
to which it has defeended. When the bucket is drawn 
up, a mercurial thermometer fixed in it is examined ; but 
great care muft be taken to obferve the degree at which 
Ifhe mercury (lands, before the lower part of the thermo¬ 
meter is taken out of the water in the bucket, left it be 
alfefled by the different temperature of the air. In or. 
der to keep the bucket in a right pofition, there are four 
cerds fixed to it, reaching about three feet below it ; to 
which the finking weight is fixed. The refult of feveral 
trials with this gage was, that, when it was let down to 
different depths from 360 feet to 5346 feet, in lat. 25. 13. 
N. and Ion. 25. 12. W. it was difeovered by the thermo¬ 
meter, that the cold increafed gradually in proportion to 
the depths, till it defeended to 3900 feet, viz. near three- 
fourths of a mile, whence the mercury in the thermo¬ 
meter came up at 53°; and though it was afterwards funk 
to 15346 feet, which is a mile and 66 feet, if came up no 
lower: the warmth of the y/ater upon the furface, and 
that of the air, was all that time 84®. When the water 
in the bucket was become of the fame temperature with 
that on the furface of the fea, equal quantities of both 
Voc, VlII. No. 492. 
G K. Id.y 
were weighed and tried by the hydrometer ; that from 
below was found to be die lieavielhand confeqiiently tlie 
falreft. 
Dr. Hales was probably led to the conflruftion of this 
fea-gage, from that invented by Dr. Hook, for the fame 
purpofe. This is exhibited in the eiigraving at fig. 3, 
It confifis of a fquare bucket C, whofe bottom and lid 
are fo contrived, that as the weight A (inks the iron B, 
to which the bucket C is faftened by two handles 1 > D, 
on the end of which are llie moveable bottoms or valve.s 
E E, and thereby draws down the bucket, the refi(lance 
of tlie water keeps up tlie bucket in tb.epoftnrc C, vvlmte. 
by tlie water, wliilft tlie bucket is defeending, (i.itb a free 
paflage through it; wliereas, as foon as il’.e bucket is 
pulled upwards by tlie line F, the reliftance of the water 
to that motion beats the lid downwards, anti keeps; it in 
the pofture (hewn at G, w hereby the included water is 
kept from getting out, and the ambient water prevented 
from getting in. Phil. Tranf. No. 9. p. 149. and No. 24,^ 
p. 447. or Abr. vol. ii. p. 26c. 
3. The Aoueo-Mercurial Gage. An apparatus 
contrived by Dr. Hales; and applied in various forms to 
the branches of trees, in order to determine the fo-rce with 
which they imbibe moifture. Let e, r, fig. 4, be a cyliu- 
dric glafs, of an inch, diameter within, and eight inches 
long. Into this glafs is introduced the branch of a young 
tiniving tree Z>, about three feet long, w ith lateral branch¬ 
es; the diameter of the tranfverfc cut i, being three- 
fourths of an incli. Having fitted the joint r to the tube 
at r, by folding’a piece of (beep’s ficin round tlie ftem, it 
is cemented with a mixture of bees-wax and turpentine 
melted together, in fuch a proportion as to make a very 
ftift'clammy pafte when cold, and over tlie cement folds 
of wet bladders are bound firmly witli packthread. To 
the lower end e of the large tube, a fmaller tube ze is 
cemented, being about one-fourth of an inch diameter, 
eighteen inches long, and full one-eighth of an inch thick. 
Thefe tubes are cemented together at e with common 
hard brick-duft or powdered chalk cement, and the joint 
is farther fecured with the cement of bees-wax and tur. 
pentine, over which a wet bladder is bound. The ap- 
paratiis being thus prepared, the branch is turned down¬ 
wards, and the glafs-tube upwards, and then both tubes 
are filled witli water; with the finger applied to the open 
end of the fmall tube, it is inverted and immerfed in the 
glafs ciftern x, full of mercury and water. In this fitn, 
ation the lower end of the branch was immerfed fix inche!< 
in water, viz. from r to f; the water was imbibed by the 
branch at its tranfverfe cut t; and, during its afeent into 
the fap-veflTels of the branch, the mercury rofe in the 
tube e z from the ciftern x, fo that in half a'n hour it was 
rifen five inches and three-fourths high, as far as z. The 
height of the mercury indicated, in fome meafure, the 
force with which the fap was imbibed, though not the 
whole force; becaufe, while the water was imbibed by 
the branch, its tranfverfe cut was covered with innumer¬ 
able little hemifpheres of air, and many air-bubbles if- 
fued out of the fap-veflTels, which partly filled the tube 
er, as the water was drawn out of it ; and, therefore, the 
height of the mercury could only be proportionable to 
the excefs of the quantity of water drawn off above the 
quantity of air which ifliied out of the wood, If the 
quantity of air ilfuing from the wood had been equal to 
the quantity of water imbibed, it is plain that the mer¬ 
cury could not rife at all, becaufe there would be no room 
for it in the tube : but if nine parts in twelve of the wa¬ 
ter be imbibed by the branch, and only three fuch parts 
of air ilfue into the tube in the fame time, the mercury 
nTUft rife near fix inches, and fo proportionably in other 
cafes. Dr. Hales obferved, that the mercury rofe higlieft 
when the fun was clear and warm, and that it fubfided 
three or four inches towards evening, but rofe again the 
next day as it grew warm, though feldom fo high as at 
firft. Dr, Hales adapted the fize and Ihape of the glafs 
apparatus to a great variety of branches of feveral Tizes 
tl» 
