50 
DISCOVERIES RELATING TO THE PRISMATIC SPECI'EA. 
TI>e ternperaf nre increaspil £jrniluallv in tlie 
centre of the heap, although externally it 
became quite coldanrl hrittle. In four honrs, 
in fact, a thermometer thrnst into the centre 
of the porous mass irulicated a temperature 
of 400“ ; a good deal of va[)onr w as now given 
off, and the adhering rosin in tlie heated paits 
began to acquire a high colour ; the smell 
conld be perceived at a considerable distance 
from my premises; it was a mixed smell of 
pitch and rosin. 
The chip cake, in this expeiiment, was 
first exposed to the air at one o’clock in 
the afternoon, and, though it rained during the 
night, at half pasteleveu the following morning 
it burst into a flame. 
In a second experiment, f placed the chip 
cake in an open tar barrel, having three lioles 
bored in tlie bottom, about two inches diameter 
each, and it did not take fire till the exiiiration 
of thirty six hours: bat the temperature of the 
mass was liiwered by removal from the wire 
strainer to the barrel, and besides, 1 am of 
opinion the limited access of air retarded the 
combustion. 
In a third trial whicii I made, combustion 
look place in five hours; hut in f Iris experiment 
the temperature of the boiiing rosin drawn 
from the still was 260^, and the chip cake w as 
laid, as in (lie first experiment, on the wire 
serren; tiie wind, too, was very high. 'I'he 
screen, in this case, was raised a few inches 
from the ground, in order to let the rosin, as it 
melted, drip away, which it did in ahundanre. 
It appeared to me as iftl e porous mass be- 
came slowly red hot. in the centre, like a 
pyrophorous, arid as if the vapour and gaseous 
matter arising from the decomposed rosin which 
lay immediately beneath, were inflamed on 
coming in contact with it. I was standing by 
when it suddenly burst into flame, and I tliought, 
■at the time, had the melted rozin been peimifteri 
to drop into water, or bad it (alien to such a 
distance as not to be kept liquid by ti e radiant 
beat from the red hot mass above, that there 
would have t een no flame, but silent com- 
bustion. 
I have since learned from Mr. Price, in 
whose distillery it has always been the prac- 
tice to put the unstrained turfientine into the 
still that lie was well aware of the fact which 
it is tlie object of this paper to record, from a 
fire having occurred several years ago on ids 
premises, w hen in the po-session of his pre- 
decessor, Mr. James Price, and that, ever 
since, they cool down the chip cake, imme- 
diately on removal from the still, with water, 
and alterwards use it as luel under the still. 
An instance of sponfaneons combustion oc- 
curred with my friend Mr. Philip Cofley, ofthe 
Dock Distillery, which is worth relating while 
on this subject. 
He bad made a quantity of the mixture used 
in theatres for producing red light, a powder 
consisting of nitrate of strontion, sulphur, 
chlorate of potash, and sulphuret of antimony 
withalitlle lampblack- A paper parcel of 
this “ red fire,” of about a pound or tw’o by 
weight, was left by him on a siielf in a store- 
room where there was no fire nor card e lights; 
f he fuilovr iiig day, while reading in an adjoin- 
ing room, he perceived a smell as if some of 
tliis powder were burning, and, on examina- 
tion, lie tound it had ignited spontaneously on 
the shelf and was actually consumed. 
M. Scan LAN. 
Sir John Eogerson*s Quay, Dublin, 29th 
June, 1835. 
ON AN EASY METHOD OF MEASUR 
ING PRISMATIC SPECTRA. 
By Mr. Andrew^ Pritchaud. 
It may be questioned whether any important 
discovery relating to the prismatic spectrum 
formed by decomposing common light, has 
been announced, since that of its heterogene- 
ous nature by the illustrious Newton, with the 
exception of the synchronical detection hy 
Wollaston and Fraunhofer, of the constant 
dark lines which were found in every instance, 
to maintain a fixed and determinate distance 
from each other. 
The, actual measurements and relative ex- 
tents of the intervening spaces, may thus be 
considered as imi)Ortant data; and any con- 
trivance, however simple, for determining 
tlieir exact places, will be. it is presumed, 
acceptible to the practical observer. I 
therefore propose to describe a very facile 
method of effecting this purpose, prefixing a 
brief account of Fraunhofer’s telescope for 
viewing and examining the spectrum. This 
telescope has a small achromatic object glass 
close before which is placed a short prism, 
one side of it making a small angle with the 
axis of the instrument. For viewing the image 
a positive eyepiece is employed, producing a 
magnifying power of between twenty and tiiir- 
ty times. In other respects it resembles a 
small astronomical telescope, having however 
a much longer range of adjustment, so as to 
render the image o( a near object distinct. Now 
the method employed by me of obtaining the 
measurement, consists simply in the addition of 
a circular glass micrometer, placed at the focus 
ofthe object glass, it being obvious to every 
person acquainted with a telescope, that a se- 
ries ofpqual divisions placed in the plane ofthe 
focus of tlie eye-glass, w ill measure the rela- 
tive distances occurring between the several 
dark Hues in the spectrum, the places of great- 
est intensity of the dilferent tints, or anv 
other phenomena that may present themselves. 
By drawing equi-fiistant and similar lines upon 
paper, the image presented by the spectrum 
may be laid down with the greatest accuracy, 
or indeed when the colours ate sufficiently 
vivid, they may at once be thrown on the pa- 
per by a camera lucida ej e-piece. 
The micometers used by me are discs of 
glass, with ifom 50 to 100 divisions to the inch, 
and are similar in construction to (hose em- 
ployed with my microscopes, except in the 
omission of the cross lines which are drawn 
upon the surface ofthe latter. 
263 Strand, near Temple Bar, June. — Records 
General Science, 1835. 
