SCIENTIFIC SUMMARY, 
327 
considering the purposes to which it might he applied or the principles which 
it might tend to elucidate.’ Indeed, this peculiarity receives abundant 
confirmation from his own words ; thus, in the Bakerian Lecture, he says : 
1 Nor is it absolutely necessaiy in this instance (in speaking of the proofs to 
be adduced in support of the undulatory theory of light) to produce a single 
new experiment for of experiments there is already an ample store ; ’ and 
in a letter written in November 1827, to his sister-in-law, Mrs. Earle, on the 
respective honours given by Herschel, in his ‘ Optics,’ to Young and Fresnel, 
•he says: ‘ And acute suggestion was then, and indeed always, more in the 
line of my ambition than experimental illustration.’ Young carried his 
opinion of the secondary importance of experiment so far as even to object 
to the increase of the fund left by Wollaston to the Royal Society to aid 
experimental inquiries, in these words : ‘For my part, it is my pride and 
pleasure, as far as I am able, to supersede the necessity of experiments, and 
more especially of expensive ones.’ ” 
Intermittent Ebullition. — Dr. I. L. Phipson, writing in the 11 Chemical 
News ” (April 23), states “ that water strongly acidified with hydro- 
chloric acid, and containing a small quantity of benzol, was found to enter 
into violent ebullition every 60 seconds ; after a while the boiling ceased 
completely, and then recommenced suddenly every 30 seconds for some time. 
The flask still being kept over the spirit lamp, the periods between quies- 
cence and violent ebullition dropped to 20, 10, and finally to 8 seconds, at 
which interval the phenomenon continued for some considerable time. The 
temperature of the vapour in the flask was 101° C., in the liquid 103-5° C., 
during the whole time of the experiment. When methyl alcohol was 
added to the above mixture of water, hydrochloric acid, and benzol, and the 
flask placed over a spirit lamp, no ebullition at all occurred for a very long 
space of time, and then it took place very suddenly, and continued.” 
A Hew Form of Auxiliary Air-pump . — At the meeting of the Physical 
Society on April 24, Mr. J. Barrett exhibited an “auxiliary air-pump” 
which is a modification of Poggendorff’s arrangement for obtaining a Torri- 
cellian vacuum, and is also allied in principle to the exhauster used by 
Geissler in the preparation of vacuum tubes. The following is a description 
of the instrument, but it is difficult to explain its action without the aid of 
a diagram : — A cylindrical glass vessel, containing about 60 lbs. of mercury, 
is connected by a glass tube, f of an inch in diameter, with another similar 
vessel, which is placed about 18 inches above it. The upper vessel is divided 
near the top into two parts, which are connected by a short neck. The tube 
communicating with the receiver passes into this vessel, and is alternately 
opened and closed below the neck, as the mercury rises and falls, by a 
floating valve. This upper vessel is in permanent connection with a glass 
vessel at the back of the instrument, which is rendered vacuous in the ordi- 
nary way, and the mercury keeps its place in the upper vessel until the lower 
one is rendered vacuous by the air-pump.* A platinum valve in the back of 
the upper vessel retains a certain quantity of mercury, when the bulk of the 
mercury (with which the whole vessel is filled at the commencement of 
operations) falls by its weight into the lower vessel, which, as has been 
stated, is rendered vacuous by the air-pump. The interval between the two 
volumes of mercury is a Torricellian vacuum, into which the residual air 
