I876.J 
The British Association . 
547 
slight exception, till July, augmenting again till the end of the year, Dr. 
Andrews passed to the subjedt of eledtricity ; he announced the failure of a 
recent attempt to deprive Oerstedt of his great discovery. To Franklin, 
Volta, Coulomb, Oerstedt, Ampere, Faraday, Seebeck, and Ohm he ascribed 
the fundamental discoveries of modern electricity. In its applications the 
names of Davy, Wheatstone, Morse, and Thomson are prominent. In connec- 
tion with the theory of eledtrical and magnetic adtion we find! the names of 
Poisson, Green, Gauss, Weber, Helmholtz, Thomson, and Clerk Maxwell. 
Among recent inventions is mentioned Prof. Tait’s discovery of consecutive 
neutral points in certain thermo-eledtric jundtions; De la Rue and Muller’s 
chloride of silver battery giving freely sparks through cold air, which, when a 
column of pure water is interposed in the circuit, accurately resembles those 
of the common eledtrical machine. The length of the spark increasing nearly 
as the square of the number of cells, it has been calculated’that with 100,000 
elements of this battery the discharge should take place through a distance 
of no less than eight feet in air. 
Reference was made to Newton’s grand investigation of the properties 
of light ; to Lord Rosse’s discovery that the surface of the moon 
facing the earth passes, during every lunation, through a greater range of 
temperature than the difference between the freezing and boiling points of 
water; to Prof. Stokes’s discovery of the cause of epibolic dispersion, in 
which he showed that many bodies had the power of absorbing rays of high 
refrangibility, and of emitting them as luminous rays of lower refrangibility ; 
to Mr. Crookes’s experiments on repulsion caused by radiation ; and to the 
discovery by Mr. Willoughby Smith of the power of light in diminishing the 
eledtrical resistance of selenium. This property has been ascertained to 
belong chiefly to the luminous rays on the red side of the spedtrum. Lord 
Rosse observed that the adtion appeared to vary inversely as the simple dis- 
tance of the illuminating power, and the accuracy of this observation has 
since been confirmed by Prof. W. G. Adams. 
In welcoming General Menabrea as a distinguished representative both of 
the kingdom of Italy and Italian science, Dr. Andrews spoke of his great 
work on the determination of the pressures and tensions in an elastic system, 
the principle being stated in the following words : — “ When any elastic system 
places itself in equilibrium under the adtion of external forces, the work 
developed by the internal forces is a minimum.” He then referred to the 
mechanical integrator of Prof. J. Thomson, in which motion is transmitted, 
according to a new kinematic principle, from a disc or cone to a cylinder 
through the intervention of a loose ball ; to Sir W. Thomson’s machine forthe 
mechanical integration of differential equation of the second order, and also 
to his tidal machine, by means of which the height of the tide at a given port 
can be accurately predidted for all times of the day and night. 
The attraction-meter of Siemens was mentioned as an instrument of great 
delicacy for measuring horizontal attractions, which it is proposed to use for 
recording the attractive influences of the sun and moon, upon which the tides 
depend, and by means of Mr. Siemens’s bathometer, in which the constant 
force of a spring is opposed to the variable pressure of a column of mercury, 
the depth of the sea may be approximately ascertained without the use of a 
sounding-line. 
The President then remarked that it was often difficult to draw a distindt 
line of separation between the physical and chemical sciences ; and it was 
doubtful whether the division was not really an artificial one. The chemist 
could make no large advance without having to deal with physical principles ; 
and to Boyle, Dalton, Gay-Lussac, and Graham were due the discovery of the 
mechanical laws which govern the properties of gases and vapours. Some of 
these laws had of late been made the subjedt of searching inquiry, which had 
fully confirmed their accuracy, when the body under examination approached 
to what had not inaptly been designated the ideal gaseous state. But when 
gases were examined undei varied conditions of pressure and temperature, it 
was found that these laws were only particular cases of more general laws, 
and that the laws of the gaseous state, as it exists in nature, although they 
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