February 15, 1873.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
G55 
[The lecturer then described and exhibited on the screen 
the principle of Dr. Young’s eriometer.] 
Our next name is that of Davy, an account of whose 
•discoveries would require a volume, and a hare recital of 
them would he long. I quote the following notes from 
the pen of our Secretary, and wish that he had been here 
to give life to the dry hones. 
In 1806, when twenty-eight years of age, Davy did 
the work which formed his first Bakcrian lecture, ‘ On 
the Chemical Agencies of Electricity.’ Six years pre¬ 
viously he had written, “ Galvanism I have found, by 
numerous experiments, to be a process purely chemical.” 
In the interim, water had been decomposed by electricity, 
and Davy began his researches with an inquiry into the 
changes produced in water by electricity. His main 
conclusion was that “ the kind of polarity of each element 
determined the electrical and chemical actions shown by 
it.” The French Academy awarded him a medal for this 
work; and from these discoveries the fame of our labora¬ 
tories took its rise. 
The next year Davy began a new series of experiments 
on polarity. He exposed different substances to the 
notion of platinum wires coming from a battery of 100 
cells ; and on October 6th he wrote in his note-book, 
Remarkable phenomena with potash.” On the 19th 
he made the following entry:—“A capital experiment 
proving the decomposition of potash.” He worked at the 
decomposition of other alkalies until the 23rd Novem¬ 
ber, when he was attacked by a fever which proved 
nearly fatal to him. 
The importance of these decompositions to the recent 
science of spectral analysis, although not dreamt of at 
.the time, can hardly be overrated ; and I will therefore 
venture to interrupt my narrative for a moment by an 
experiment,—a very well-known one, with a slight 
modification, which wall serve to illustrate the point. 
£The speaker then exhibited the dark absorption-line of 
sodium; but so arranged as to show the dark line in the 
ventre of, and not entirely obliterating, the bright line; 
proving that a certain density of vapour is necessary for 
complete absorption.] 
In 1808 Davy began to work on the composition of 
muriatic acid; and with a new battery, provided for him 
by subscription, he attacked different substances with in¬ 
creased energy. In 1810 he sent to the Royal Society 
his researches on oxymuriatic acid and the elements of 
muriatic acid, on what is in fact now known as chlorine. 
In 1811 he made the acquaintance of Mrs. Appreece, 
and in 1812 wrote to his brother, “ In a few weeks I 
shall be able to return to my habits of study and research. 
I am going to be married to-morrow, and have a fair 
prospect of happiness with the most amiable and intel¬ 
lectual woman I have ever known.” The issue of these 
hopes has been written by his biographers; but the dis¬ 
appointment of the last seventeen years of his life is 
illuminated by the invention, not less original in its con¬ 
ception than benevolent in its object, of the Safety 
Lamp. 
The great value of this contrivance, and of questions 
arising out of it, will, I trust, be sufficient apology for 
diverging again from my story in order to mention some 
very important experiments now in progress by Mr. 
Galloway. Explosions, it is well known, occur even in 
cases where the safety lamp is used. And it has been 
noticed that in these cases they occur most frequently 
after the firing of a blasting shot in the neighbourhood; 
and as it was almost certain that the penetration of the 
fire-damp through the gauze of the lamp was not due to 
a sudden flow of gas from one part of the mine to 
another, experiments have been instituted to determine 
whether the transmission of the sound wave, or wave of 
compression, may not have been the means of producing 
the mischief. Through the kindness of ^lr. GallQway 
we have here a tube arranged for making such an ex¬ 
periment. At one end there is the inflammable current 
enveloping a safety lamp; in the centre is a loose 
diaphragm, and at the other end a pistol will be fired, by 
the explosion of which a sound wave wall be propagated 
along the tube. On the arrival of the sound wave at the 
extremity of the tube, the combustion will penetrate the 
safety lamp. But I here leave the matter in the hands 
of Mr. Galloway, of whose experiments wo hope to hear 
more hereafter. 
Of the next great name connected with our institution, 
namely, Michael Faraday, of his life and his discoveries 
the history has been already written, so far indeed as it 
can be written, by Bence Jones, by Tyndall, and by 
Gladstone. “ Si monumentum quseris circumspice.” These 
volumes of notes, from 1831 to 1856, will give some idea 
of the amount of work which he did in our laboratory ; 
and their value will be better appreciated through the 
consideration that before these notes were made, no less 
than sixty of his scientific papers had been printed, nine 
of them in the ‘ Philosophical Transactions.’ 
Those of us who were present at Tyndall’s two me¬ 
morable lectures on “ Faraday as a Discoverer,” are not 
likely to forget the impression of the man left by them 
on our minds ; and for those who were not present, it 
would be an office thankless to your lecturer and bur¬ 
densome to his hearers, to contribute a feeble reproduc¬ 
tion of those life-like memoirs. For our present purpose 
it will be sufficient to say that the entire fabric of those 
brilliant and manifold contributions to human know¬ 
ledge were wrought out within the walls of the Royal 
Institution. 
His great experiments have been so often and so well 
exhibited in this theatre, that some apology is needed 
for bringing any of them before you again ; but in re¬ 
peating for my own instruction some of those which 
bear more particularly upon the subject of light, I have 
been tempted to reproduce one of them here. In doing 
this I have been perhaps moved more by a fascination of 
the phenomenon, and by a piece of instrumental good 
fortune which enables me to introduce an old friend 
under a new garb, than by any better reason. The ex¬ 
periment in question is that which Faraday called <£ the 
magnetization of light, and the illumination of the 
lines of magnetic force ; ” we should now term it the 
rotation of the plane of polarization under the influence 
of the magnetic field. But in order that we may not 
even by inadvertence confuse the rotation here produced 
with that due to quartz, or oil of turpentine, I will 
draw your attention, by way of memorandum, to the 
nature of the magnetism produced by spiral currents in 
given directions, and of the rotations of free currents 
produced by magnets. 
[The lecturer then showed the opposite rotations of 
two sparks discharged about the two poles respectively 
of an electro-magnet, and the reversal of those rotations, 
first by a change of the poles, and secondly by a reversal 
of the direction of the sparks.] 
You now see upon the screen an image of the figures 
produced by a magnificent piece of heavy glass under 
the action of polarized light. Its size enables me to 
make use of about four times the amount of light usually 
available in this experiment; and I have taken advan¬ 
tage of the figv>re which it3 imperfect annealing pro¬ 
duces, to vaiy the effect upon the screen. I he dark 
parts of the figure indicate the parts of the beam in 
which the vibrations are perpendicular to those trans¬ 
mitted by either polarizer or analyser, and which are 
consequently cut off. Now if anything should intervene 
to change the plane of those vibrations a portion of them 
will be transmitted, and a partial illumination of the 
screen will ensue. This turning of the plane of vibration 
is effected by the magnet as soon as its force is de¬ 
veloped by the electric current sent through its coils. 
[The lecturer then ‘‘dispersed” the dark lines of tho 
figure .by means of a platfe Qf q uar tz > an( ^ a ^ cr turning 
polarizer and analyser so as to colour the centre o£ t e 
field with the tint intermediate between red and violet 
(teinte sensible ), he showed that when the magnet was 
