Mov. 3, 1881] 
NATURE 
21 
experience of several years showed that there was something like 
an annual inequality of level. There were sometimes changes 
through 2” or 3” which took place in a few hours. : 
Att Geneva M, Plantamour has been making observations con- 
cerning variations of the plumb-line, by means of delicate levels, 
and has arrived at results in general accordance with those of M. 
d’Abbadie. 
The experiments of the authors present a general confirmation 
of these conclusions, and show that the earth’s surface is in a state 
of continual movement. 
With reference to this continual oscillation the authors adduce 
an experiment which was commenced about three and a half 
years ago by Mr. Horace Darwin at Down, in Kent. The ex- 
periment was undertaken in connection with Mr. Darwin’s 
investigation of the geological activity of earthworms. There 
are two stout metal rods, one of iron and the other of copper. 
The ends were sharpen d, and they were hammered down verti- 
cally about eight feet deep into the soil, and they are in contact 
with one another, or nearly so. The ends were then cut off 
about threeinches above the ground. 
A stone was obtained like a small grindstone, with a circular 
hole in the middle. This stone was laid on the ground with the 
two-metal rods appearing through the hole. An arrangement 
with a micrometer screw enables the observer to take contact 
measurements of the position of the upper surface of the stone 
with regard to the rods. The stone has, on the whole, always 
continued to fall, but the general descent can only be gathered 
from observations taken at many months apart, for it is found 
to be in a state of continual vertical oscillation. 
The measurements are so delicate that the raising of the stone 
produced by one or two cans full of water poured on the ground 
can easily be perceived. The effect of frost and the wet season 
combined is strongly marked, for on January 23, 1881, the stone 
was 4°12 mm. higher than it had been on September 7, 1880. 
The prolonged drought of the present summer has had a great 
effect, for between May 8 and june 29 the stone sank through 
5°79 mm, 
The changes produced in the height of the stone are, of course, 
entirely due to superficial causes ; but the amounts of the oscil- 
lations are certainly surprising, and although the basements of 
astronomical instruments may be very deep, they cannot entirely 
escape from similar oscillations, 
The last part of the paper contains a discussion of the present 
aspects of the question, and a criticism of the various forms of 
instrument which have been used hitherto for the detection of 
small variations in the position of the plumb-line, 
The authors suggest that greater precautions should be taken 
in the protection of the piers of transit instruments from changes 
of temperature, and in the drainage of the soil round the base- 
ments of the piers ; they also draw attention to the disturbing 
effect of the weight of the observer’s body. They express a 
hope that systematic observations of changes of level may be 
undertaken at a number of observatories by some instrument 
analogous to that with which they are working. They are still 
prosecuting their experiments, and they are in hopes of being 
able to reduce their instrument to a convenient form, so that it 
may not be difficult to transport or to erect. 
Tn conclusion they state that they have no hope of being able 
to observe the lunar attraction in the present site of observation, 
but they think it possible that they may devise a portable instru- 
ment which shall be amply sensitive enough for sucha purpose, if 
the bottom of a deep mine should be found to give a sufficiently 
invariable support for the instrument. 
AN ERROR IN THE COMMONLY ACCEPTED 
THEORY OF CHEMISTRY 
At a public meeting of the University College Chemical and 
Physical Society Prof. A. W. Williamson, F.R.S., gave 
an address on “‘ An Error in the Commonly Accepted Theory of 
Chemistry.” 
He began by saying that he had been frequently struck by the 
fact that two theories believed at one time to be conflicting had 
often been shown by the progress of study to be both true. As 
an instance in point he took the rival theories, one of which 
represented m)lecules as constituted after the pattern of three or 
four types, while the other viewed them as containing complex 
groups called radicles 
There was at one time opposition between those who made 
use of atomic weights and those who employed equivalent 
weights ; the most important step that has of late been taken 
is the introduction of the notion of equivalence into the atomic 
theory; an inspection of the series HCl, H,O, H,N, HyC 
showed that the atom of chlorine has a different value to that of 
oxygen, nitrogen, or carbon; thus ammonia may be viewed as 
being formed by replacing three atoms of chlorine in three 
molecules of hydric chloride by one atom of nitrogen. Thus 
nitrogen was said to be trivalent or a triad, and other elements, 
such as phosphorus, boron, &c., were found to resemble it in 
this respect ; oxygen was called a dyad, and it was found that 
sulphur, calcium, &c., might also be classed as divalent; in 
short every element might be placed in one or other of the 
groups, monad, dyad, triad, &c. ‘That an element can belong 
to one only of these groups was the view still held by one dis- 
tinguished chemist, who, for instance, said that nitrogen was 
trivalent only, and that in sal-ammoniac it was not pentavalent, 
but that the body in question was a molecular compound of two 
che nical compounds, ammonia and hydric chloride. 
He (Prof. Williamson) thought this was little else than a 
return to Berzelius’ mode of representing compounds, though it 
was open to an objection from which the theory of the Swedish 
chemist was free; for Berzelius said that the force which 
united the two molecules that) made up the compound mole- 
cule was identical with that which held together the atoms of 
the constituent molecules, the force being in each case electrical ; 
whereas Prof. Kekulé assumes the forces in the two cases to 
differ, the one being molecular, and the other chemical. 
Now as long as we knew neither of these forces, he (Prof. 
Williamson) thought it hazardous to assert that there was a 
difference between them. A study of the evolution of heat in 
chemical processes threw some light on the su'ject; Berthelot 
and Thomsen had shown that when you placed a number of 
substances within the influence of one another, that reaction or 
decomposition took place which could evolve the most heat, and 
we must take into account not merely the heat given out by 
what we considered the purely chemical process, but also that 
due to the passage of the product from one state of aggregation 
to another—from the liquid to the solid state when a precipitate 
was formed. 
Thus the chemical process was determined by the-heat-due-to 
the chemical reaction plus that due to change of physical con- 
dition; and this indicated an identity between chemical and 
physical force, We might learn the same lesson from Deyville’s 
truly remarkable researches on dissociation or s‘rictly reversible 
decompositions. Thus calcic carbonate was decomposed by 
heat into lime and carbonic acid, but no sooner was the temper- 
ature sufficiently lowered than the two recombined ; so, when 
water was heated, the molecules were separated and formed 
steam, but on lowering the temperature they recombined to 
produce water. Ice, water, and steam had in many respects 
different properties—differences in specific gravity, specific heat, 
refractive power, &c., quite analogous to those which were found 
between different chemical compounds. 
We had therefore no grounds for assuming a difference between 
chemical and physical force ; Kekulé’s theory that an atom can 
have one, and only one, atomic value was no longer tenable, for 
it involved the assumption of molecular compounds. The theory 
commonly in vogue was that atoms vary in their value within 
certain narrow limits; that nitrogen, for instance, was either 
trivalent or pentavalent. It had even been asserted that the com- 
bining power of an atom was independent of the nature of the 
elements with which it combined; in the words of a very distin- 
guished chemist, “No matter what the character of the uniting 
atoms may be, the combing power of the attracting element is 
always satisfied by the same number of these atoms.” This view 
appeared to him (Prof, Williamson) to have been due to a habit 
of mind naturally prevailing in many studies, but which, he 
thought, we had found reason in our scientific work to abandon 
—he meant the absolute as opposed to the relative. 
Prof. Williamson then went on to say that he knew of no 
limitation to atomic value ; he did not say there were no limita- 
tions, but he did know that many elements have atomic values 
greater than those commonly assumed. 
We found that the character of the atoms materially affected 
the result ; thus gold could not combine with more than three 
atoms of chlorine alone, but it could take up an additional atom 
of chlorine if supplied with an atom of sodium at the same time. 
In this way we got the common double chloride of gold and 
sodium, NaAuCly, in which the gold is pentavalent. 
We were not t> consider the sodium as being here combined 
