152 
tremity, the maximum of velocity of 
the needle takes place at the south 
face of the. object, and, the minimum at 
the north face. 
It has been, hitherto, conceived, that 
in erystals which separate light into. two 
fasciculi (partitions) one of them con- 
forms to the laws of ordinary reftac- 
tion. M. Fresnel admits of this prin- 
ciple, as correct with respect to cris- 
tals of one axis, but: rejects it in those 
of two, whose radiations vary in velocity 
and refraction, like, those of the. extra- 
ordinary kind, but are confined within 
narrower limits. 
The oxy-hydrous blow-pipe, invented 
by Dr. Hare, in America, in 1802, and 
which the late Dr. Clarke, of Cambridge, 
since somewhat improved upon, in point 
of safety to the operator, whilst repeat- 
ing and extending’ the experiments of 
Dr. Hare * therewith, has lately been fur- 
ther improved, by Professor Gurney, of 
London, who kas apparently rendered 
this most potent of agents’ in the hands 
of the chemical operator, quite safe to 
himself and the spectators, which was 
very far from the case, even after the 
improvements of Dr. Clarke and others. 
Oxygen and hydrogen gases, when mixed 
in the exact. proportions by bulk or 
weight, proper for formidable water, in- 
the magazine of one of these blow- 
pipes, through whose orifice it was to’ 
be ‘expelled with force, has been found 
very liable to explode very dangerously 
to all persons near, owing to the flame’ 
receding imwards, immediately on any’ 
considerable diminnition of the pressure 
and velocity of the jet of gas, and 
thereby exploding ‘the magazine: and 
this retrogression of the flame has not 
invariably been prevented by using the 
smallest ‘practicable diameter of jet, or 
(any more than explosions in coal-pits, 
have been prevented) by the addition of 
interior screens of the finest wire- 
Gauze. 
Professor Gurney, therefore, since ve- 
rifying these facts, and well considering 
the subject, has constructed his gas ma- 
gazine, ‘not: of iron’or copper, whose 
fragments in the event. of explosion, 
were the chief cause of mischief, but 
of a bladder, or bag of varnished silk, 
pressed upon by a pasteboard cover; as 
lightly constructed as' the requisite pres» 
* The. “ Philosophical Magazine” of Mr. 
Tilloch, vol. 14, contains a detailed account 
of Dr. Hare’s original experiments, on va- 
rious substances exposed to the inflamed jet 
of his oxy-hydrous blow-pipe. 
Spirit of Philosophical Discovery. 
[Sept: 1; 
sure will permit; and connected only: 
by strings for effecting the pressure, by: 
drawing down the cover, upon the solid: 
parts of the apparatus beneath. From 
this. flexible magazine, the gas passes 
through a pipe, not immediately, to the 
jet, but into a small strong safety cham- 
ber, the lower part of which contains 
water, only partly filling it, and its top 
is only closed by a good cork; the last 
mentioned pipe being bent down, so as 
to deliver its gas: beneath the water’s sur- 
face: and from above the water, another 
small pipe, intercepted by a succession 
of fine wire-gauze screens, conducts the 
mixed gas to the jet. Hitherto, no ac~ 
cident has attended. the frequent use of 
this simple apparatus, nor does there 
appear to us, any source of danger 
which is not provided against. The ac- 
count of Professor Gurney’s “ Lectures 
on Chemical Sciences,” lately published, 
minutely describes the above apparatus 5. 
and another, wherein the gazeous pro- 
ducts of the combustion caused by this 
blow-pipe may be preserved for chemical 
examination. 
Determination of the Names of the Mole- 
cules of Bodies. 
Mess of the 
Molecules ; 
Substances. that of (xy gen: |: 
being taken | 
at Unity, 
Hydrogen ......-+6: 0.0624 
OXYGEN woe ce eee es TET; 
t WWAteD aps sic 'dmroce orreen® 1.1248 
ZORC a seeeMe da sient 0.878161 
Chiomne ... seer aicr 2.2535 
Carbon) 0 Stes we --'s 0.75392 
Sulphur .........+-- 2.2447 
Pluorimms:o%. Se. ose 1.125 
F Boriuny Oks ee lees eel . 0.921 
Potassium... +... 4.89915 
Sodium wise .ns cawen bir S184 
Galeinna s)he clete sia 5.1206 
Magnesium... +. ...+++ 6.3344 
Bora, A.«ijeeresh- nels) LG ees 
Strontium ...c...++.. -} 10.946 
STICHUM: 6.0.2 epee ae 1.976] 
' Aluminum ........ 2.2822 
Mercury ..-....---- . | 25.316 
MSUIVEL se clanaclot ge. vee | 13.51605_ 
Gold POL UGS eee 
O Platina eve cee tages | 24.30452 
 Beadivics bole. ais owlaca ait 28.8900. 
Tron! : ciacen soc. decdclt 883 
Copper «iassseede seen [79139 
Manganese «+ «je e008 “Zl 1575; 
Tungsten..:....<s+e- |, 2415378 
Y Fate NS 1) 5 POE Ns 8.0645 
» Molybdena ...--+-++« 5,968 
Antimony ..++++++-¢ 8.6645 + - 
4.;70385- 
 ArSeniuim “2602 esos oe 
