ON POLARIZfib LIGHT. 
493 
Hills, alluded to by Professor Phillips, 
were almost entirely conducted by Mr. 
Irvine. These observations were par- 
ticularly interesting, from the fact, that 
the mines, in consequence of a strike 
among the workmen, had not been 
worked for many months, and at the 
same time it most fortunately happened 
that they were selfdrained, that is, by 
machinery worked by external power, 
without the aid of either animals or 
steam. This most fortunate concur- 
rence of favourable circumstances, which 
could be expected to be met with in so 
very few instances, at once disembar- 
rassed the observations from many 
sources of error, which, but for this, 
would have still left considerable doubts 
of the results being, partially, at least, 
affected by the heat generated by ani- 
mals residing and working in the mines, 
as Well as artificial fires kept up for the 
purposes of ventilation or of originating 
power. It was upon these grounds that 
he perceived the importance of them, 
but had it not been for the valuable as- 
sistance afforded him by Mr. Irvine, 
who descended into the mine, and placed 
the thermometer and made the observa- 
tions, he could scarcely have been as 
successful as the results already obtained 
warranted him in hoping he should be. 
These results, which, of course, h^d 
not as y’^et reached the degree of accu- 
racy which he still looked for, lead to 
the conclusion that the temperature in 
that mine increased about 50 of Fahren- 
heit for a descent of ninety-five fathoms. 
— Professor Stevelly stated, that as prac- 
tical utility was one of the principal ob- 
jects of the British Association, he 
might be permitted to add, that the 
waters of these wells, in consequence of 
their temperature being in general ele- 
vated above the mean temperature of 
the place at which they delivered their 
waters, had been applied to the very 
important practical purpose of freeing 
machinery of ice in winter, insomuch, 
that by their instrumentalitj% machine- 
ry, such as water-wheels, &c., which 
had alwa5’'s previously been clogged by 
ice for a considerable part of the winter, 
to the great loss of the owner’s manu- 
factory, were, by the aid of the waters 
of these fountains, kept constantly free, 
while the same water had even been 
previously, in some instances, conduct- 
ed through the factory itself, with a 
view to keep up a uniform and elevated 
temperature within its walls, thus af<* 
fording a second and a very valuable 
practical application. 
The Rev. Mr. Craig now read a pa- 
per on Polarized Light. He stated, 
that he conceived the term ])olai:iza- 
tion of light” had been hastily adopted, 
and tended to mislead, by directing the 
mind to a class of phenomena, with 
which he thought the effects upon light 
were by no means to be chssed. In 
fact, he conceived that the phenomena 
usually attributed to ])olarization, were 
only particular instances of the ap])lica- 
tion of a general principle resulting 
from the very nature of light, namely, 
that light, when strong, could pass 
through the substances of several pecu- 
liarly constructed media, in a manner 
which, when its impulse has been pre- 
viously weakened, which by several 
means it may be, it could by no means 
similarly pass. The Rev. gentleman 
then exemplified in the common optical 
changes made upon the course of light, 
and called reflection and refraction, 
how rays, which before incidence had 
gone on together, were by these pro- 
cesses so separated as to produce to- 
tally separated images, and even suc- 
cessions of images ; in this and similar 
cases, he conceived that the division 
of the rays was accompanied with a 
weakening of the force of each part, 
insomuch that they would now no 
longer pass through media in the same 
way that they would have passed pre- 
viously ; and thus, in certain cases, re- 
sulted an inability to pass even through 
regular structures, such as crystals of 
Iceland spar, tourmaline, &c , without 
exhibiting phenomena arising out of 
the peculiarity of such structures, and 
which afforded diversities, as he con- 
tended, fully sufficient to account for 
all the phenomena usually denominated 
polarization. He then went in detail 
over five common methods of polariz- 
ing light : viz. 1. By reflections at cer- 
tain angles from plates of glass ; 2. By 
reflections from similar plates, having 
their under surfaces blackened, so as 
to absorb the rays upon their coming 
to the back surface of the glass, and to 
this glass he would refer the effects of 
all polished surfaces, such as varnished 
mahogany tables and trays, j apanned 
metals, burnished leather, &c., and he 
instanced the total disappearance of all 
