733 • B A R" O M 
cork will occafion no inaccuracy in the refults; for it will 
evidently require a confulerable time; through the er- 
tremely llender communications, to reftore the balance be¬ 
tween the external and internal air, if ever that balance 
can rigoroLilly obtain. Dr. Hamilton gives very copious 
and circumft'antial direiilions for theconflruftion, adjull- 
rnent, and application, of this inftrument. He remarks 
that mercury is bell cleaned by fhaking it repeatedly in a 
phial with frefh portions of water. To correct the errors 
of altitude caufed by the fluctuation of the fitrface of mer¬ 
cury in the bafon, he advifcs to compute tables from the 
proportion which the aperture of the tube bears to that of 
the cylinder. Dr. H. Hamilton, dean of Armagh, pro- 
pofes, that, as the pores of cork may in time become chunk¬ 
ed with daft or humidity, the box fliould have a top of 
ivory with a hole to drop in a floating gage, and which 
might be occafionally flopped with a peg or lcrew, to ren¬ 
der the inftrument fafely portable. Inftead of making ta¬ 
bles for correcting the error occafioned by the variation of 
the level of the mercury in the bafon, he thinks it would 
be more convenient to contract proportionally the divi- 
fions of the lcale. It isTuggefled that thefe clofe baro- 
meters would anfwer equally at lea. In reality, the very 
defects of the conftruftion of fuch inftruments prove ad¬ 
vantageous on (hip-board ; fmce, being very gradually af¬ 
fected by any change, they are lefs apt to be dilturbed by 
the working of the veflel. The profecution of this idea 
may lead to the perfection of that great defideratum, the 
marine barometer. 
The Common Chamber Weatherglass, is alfo 
ufually fitted up in a neat mahogany frame, with embel- 
lifhments, to make it an ornamental piece of furniture. 
It confifts of the common tube barometer, with a thermo¬ 
meter by the fide of it, and an hygrometer at the top, as 
exhibited in fig. 13. There is alfo a new fort of barome¬ 
ter, or ztleather vjlrument by the found of a wire. This is 
mentioned by M. Lazovvfki in his Tour through Switzer¬ 
land, where it was difeovered by accident. It feems that 
a-clergyman, though near-fighted, often amtifed himfelf 
with firing at a mark, and contrived to flretch a wire fio as 
to draw the mark to him to fee how lie had aimed. He 
obferved that the wire fometimes founded as if it vibrated 
like a mufical cord ; and that, after fuch foundings, a 
change always enfued in the (late of the atmofphere ; from 
whence he came to predict rain or fine weather. On mak¬ 
ing farther experiments, it was found that the founds 
were molt diftindl w hen extended in the plane of the me¬ 
ridian. And, according to the weather which was to fol¬ 
low, it was found that the founds were more or lefs foft, 
or more or lefs continued ; alfo fine weather, it is faid, 
was announced by the tones of counter tenor, and rain by 
thole of bafs. It has been faid that M. Volta mounted 
fifteen cords in this way at Pavia, to bring this method 
to fome precifion ; but no accounts have yet appeared of 
the fuccefs of his obfervations. This difeovery, how¬ 
ever, ferves to fhevv, how very fenfibly the ambient aits 
upon even the fmalleft conductors ; and in fome ineafure 
countenances tire obfervation of an eccentric authority, 
who fays, “ that by means of barometers we may regain 
the knowledge that (till refides in brutes, but which' we 
forfeited, by not continuing in the open air, as they moflly 
do ; and, by our intemperance and excels, .corrupting, the 
crafts of our organs of fenfe. It is from this cattle that 
the hufbandman and labourer have the advantage over 
the rich and voluptuous, in (lore of health and exuberance 
©f offspring.” 
PHENOMENA and OBSERVATIONS of the BA¬ 
ROMETER. 
The phenomena of the barometer are various ; but au¬ 
thors are not yet agreed upon the caufes of them ; nor is 
the life of it, as a weather-glafs, yet perfeftly alcertaincd, 
though daily obfervations and experience lead us dill near¬ 
er to precifion. Mr. Boyle obferves, that the phenomena 
»f the barometer are fo precarious, that it is exceedingly 
E ‘ T' E R. 
difficult to form any certain general rules concerning the 
rife and fall of the mercury. Even that rule fails which 
feems to hold the moft generally, viz. that the mercury is 
low in high winds. The bed rules however that have 
been deduced by feveral authors are as follow. 
Dr. Halley's Rides for judging of the Weather. — 1. In calm 
weather, when the air is inclined to rain, the mercury is 
commonly low. 2. In 1 'erene, good, and fettled, weather, 
the mercury is generally high. 3. Upon very great winds r 
thougli they be not accompanied with rain, the mercury 
finks lowed of all, according to the point of'the compafs 
the wind blows from. 4. The greatefl heights of the mer¬ 
cury are found upon eafterly or north-eafterly winds, other 
circumftances corroborating. 3. In calm frofty. weather, 
the mercury commonly.(lands high. 6. After very great 
florins of wind, when the mercury has been very low, it 
generally rifes again very fall. 7. The more northerly 
places have greater alterations of the barometer than the 
more foutherly, near the equator. 8. Within the tropics, 
and near them, there is little or no variation of the baro¬ 
meter, in all weathers. For in (lance, at St. Helena it is 
little or nothing, at Jamaica 3-ioths of an inch, and at 
Naples the varation hardly ever exceeds an inch ; whereas 
in England it amounts to two inches and a half, and at Pe- 
terlburg to three and one-third nearly.. Dr. Beal, who 
followed the opinion of M. Pal cal, obferves that, coeteris 
paribus, the mercury is higher in cold weather than in 
warm : and in the morning and evening ufually higher 
than at mid-day. That in fettled and fair weather, the 
mercury is higher than either a little before or after, or in 
the rain ; and that it commonly defeends lower after rain 
than it was before it. And lie aferibes thefe effects to the 
vapours with which the air is charged in the former cafe, 
and which are difperfed by the falling rain in tiie latter. 
If it chance to rife higher after rain, it is ufually follow¬ 
ed by a fettled lerenity. And that there are often great 
changes in the air, without any perceptible alteration in 
the barometer. 
Mr. Patrick's Rules for judging of the Weather. —Thefe arc 
efteemed the beft.of any general rules hitherto, given. 1. 
The riling of the mercury prefages, in general, fair wea¬ 
ther; and its falling, foul weather, as rain, fnovv, high 
winds, and dorms. 2. In very hot weather, the falling 
of the mercury indicates thunder. 3. In winter, tlie ril¬ 
ing prefages fro(l : and in frofty weather, if the mercury 
falls three or four divifions, there will certainly follow a 
thaw. But in a continued frofl, if the mercury rifes, it 
will certainly fnovv. 4. When foul weather happens f'0011 
after the falling of the mercury, expect but little of it; 
and on the contrary, expert but little fair weather when 
it proves fair fhortly after the mercury has rifen. 5. In 
foul weather, when the mercury rifes much and high, 
and fo continues for two or three days before the foul wea¬ 
ther is quite over, then expect a continuance of fair wea¬ 
ther to follow. 6. In fair weather, when the mercury 
falls much and low, and thus continues for two or three 
days before the rain comes; then expect a great deal of 
vet, and probably high winds. 7. The unfettled motion 
of the mercury always denotes uncertain and changeable 
weather. 8. You are not fo ftrictly to obferve the words 
engraved on the plates, as the mercury’s rifirtgand falling; 
though in general it will agree with them. For if it (lands 
at much rain, and then rifes up to changeable, it prefages 
fair weather; though not to continue fo long as if the mer¬ 
cury had rifen higher. And fo, on the contrary, if tlie 
mercury flood at fair, and falls to changeable , it prefages 
foul weather ; though not fo much of it as if it had funk 
lower. 
Upon thefe rules of Mr. Patrick, the following remarks 
are made by Mr. Rowning. That it is not fo much the ab- 
folute height of the mercury in the tube that indicates the 
weather, as its motion up and down : wherefore, to pals 
a right judgment of what weather is to be expected, we 
ought to know whether the mercury is actually rifing or 
falling; to which end the following rules are of ufe. 1. 
