Fan. 27, 1870] 
NATURE 34 
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BOTANY 
British Museum Herbarium 
Tue national Herbarium at the British Museum, though not 
equal in extent to that at Kew, is one of very great value to 
botanists from the numbers of ‘‘type-specimens”’ it contains ; 
that is, specimens named by the original discoverer or describer, 
thus serving as a standard for reference. According to the 
official report lately issued by the Curator, Mr. J. J. Bennett, the 
herbarium has received large and important additions during the 
past year, by purchase and donation, from all parts of the world, 
including flowering plants, ferns, lichens, mosses, sea-weeds, the 
microscopic Diatoms, fossil plants, sections of wood, &c. ; while col- 
lections previously received have been arranged and incorporated. 
Wood for Gunpowder 
ALTHOUGH the materials of which gunpowder is made have 
not varied since its first invention, there has been considerable 
variety in the kind of wood from which the charcoal has been 
obtained. Dense woods are always rejected and the lighter kinds 
chosen, especially those most free from silica, and capable of 
producing a friable porous charcoal which burns quickly and 
leaves the least possible quantity of ash; the kind now generally 
used by gunpowder manufacturers is known as ‘“ Dog-wood,”’ 
and is usually described as being obtained from the small tree 
popularly known under that name, the Cornus sanguinea. 
Dr. Hooker has, however, recently discovered that this is a popu- 
lar error, and that the wood is really almost universally obtained 
from the Buckthorn, or Rhamnus frangula; the former tree 
being now never used for this purpose, if indeed it ever was. Till 
a few years since, the bulk of the Buckthorn wood used in 
this manufacture was supplied from English plantations in 
Suffolk, Norfolk, Essex, and Kent, but the great increase 
recently in the demand for the finer descriptions of gunpowder 
has rendered this source insufficient ; and it is now cultivated 
in immense districts of forest and marsh in North Germany, 
lying between Berlin and Frankfort, where it forms the natural 
undergrowth. From the high price obtained for the wood, 
10/. to 152. per ton, its cultivation would be exceedingly lucra- 
tive in this country, as it will grow in almost any soil. 
Action of Ether on Plants 
THE action of ether as an anesthetic on the animal frame has 
induced Dr. Maxwell Masters to experiment on its effects on 
plants. He states that if a drop is placed gently on the leaf of 
the Sensitive plant, it produces a paralysing effect, rendering it 
insensible to subsequent contact. It, however, the ether impinges 
on the leaf with force, or is allowed to drop from a considerable 
height, contraction of the leaf immediately takes place, the 
impact of the falling drop counteracting any paralysing power. 
It is well known that in the contraction of the leaves of the 
Sensitive plant a certain amount of vital force is expended, and 
that if often repeated the plant becomes exhausted, and a time 
of rest is required before the phenomena are repeated. 
Viridescence of Leaves 
M. PRILLIEUX has established, as the result of a large number 
of observations on the leaves of barley, that viridescence is more 
rapid in diffused light than in the direct light of the sun, in con- 
trast to the production of oxygen, which is more abundant the 
stronger the light. He introduced into a dark chamber a pencil 
of solar rays, and, by means of a lens, produced a diverging 
cone, in which he placed the barley at different distances from 
the lens, consequently under different intensities of light deter- 
minable with precision. He found that near the lens, that is, 
placed in a very intense light, the etiolated leaves scarcely 
became green, while at a greater distance the viridescence took 
place more rapidly, and attained its maximum at a distance of 
three or four metres, beyond which the activity decreased ; so 
that in a too feeble light the effect was the same as in too strong 
alight. [L’ Institut]. 
MOLteEr has prepared a beautiful microscopic slide, containing 
300 distinct species of Diatoms, showing au extraordinary variety 
of form, and arranged with marvellous regularity. It forms one 
of the most interesting objects for the microscope we have seen. 
THE “ Prodromus Systematis naturalis Regni vegetabilis,” the 
work of three generations of De Candolles, is now approaching 
completion, as it is not intended to contmue it beyond the 
Exogens. The first section of the sixteenth volume, just pub- 
lished, includes two important monographs, the Urticacee by 
Weddell, and the Piperacee by Casimir De Candolle. 
SOCIETIES AND ACADEMIES 
LoNDON 
Royal Society, January 20.—The following papers were 
read :— 
“‘On the mechanical performance of logical inference,” by 
W. Stanley Jevons, M.A. Lon't., Professor of Logic, &c., in 
Owens College ; communicated by Professor E. Roscoe, F.R.S. 
The author first referred to the general use of mechanical contri- 
vances for the purpose of mathematical computation, and then 
contrasted this fact with the utter absence of machines for aiding 
logical operations. This absence he attributed to the incomplete- 
ness of the old logical doctrines. The problem of logical science 
in its complete generality was first solved by Boole. His logical 
views, when simplified and corrected, give us a method of indirect 
deduction of extreme generality and power, founded directly upon 
the fundamental laws of thought. A proof of the truthfulness 
and power of this system is to be found in the fact that it can be 
embodied in a machine just as the calculus of differences is em- 
bodied in Mr. Babbage’s calculating machine. To explain the 
nature of the logical machine alluded to, it may be pointed out 
that the third of the fundamental laws of thought allow us to 
affirm of any object one or the other of two contradictory attri- 
butes, and that we are thus enabled to develope a series of alter- 
natives which must contain the description of a given class or 
object. Thus, if we are considering the propositions, 
Tron is metal, 
Metal is element, 
we can at once affirm of iron that it is included among the four 
alternatives :— 
Metal, element, 
Metal, not element, 
Not metal, element, 
Not metal, not element. 
But according to the second law of thought, nothing can com- 
bine contradictory attributes, and this law prevents us from sup- 
posing that zvov can be not-meta/, whilethe first premiseaffirms that 
It is metal. The second premise again prevents our supposing that 
the combination metal, not-element, can exist. Hence the only 
combination of properties which the premises allow us to affirm 
of tron is metal, element. In a similar manner a complete 
solution of any logical problem may be effected by forming the 
complete list of combination in which the terms of the problem 
can manifest themselves, and then striking out such of the com- 
binations as cannot exist in consistency with the conditions of 
the problem. The logical machine actually constructed repre- 
sents the combination, 16 in number, of four positive terms, 
denoted by A, B, C, D, and their corresponding negatives, 
a, b,c, d. The instrument is provided with eight keys, repre- 
senting these terms when appearing in the subject of a proposition, 
with eight keys, placed to the right hand of the former, repre- 
senting the terms when occurring in the predicate of a proposition, 
and with the certain operation keys denoting the copidar of the 
proposition, the fw// stop at the end of it, and the conjunction or, 
according as it occurs in the subject or predicate. There is also 
a key denoting the fizis or end of an argument, which has the 
effect of obliterating any previous impressions, and making the 
machine a ¢abw/a vasa. If now each of the letter terms, 
A, B, C, D, be taken to represent some logical term or noun, 
and propositions concerning them be, as it were, played upon 
the machine, as upon a telegraphic instrument, the machine 
effects thereby such a classification and selection of certain rods 
representing the 16 possible combinations of the terms, that only 
those combinations consistent with the propositions remain 
indicated by the machine at the end of the operations, When 
once a series of propositions is thus impressed upon 
the machine, it is capable of exhibiting an answer to 
any question which may be put to it concerning the 
possible combinations which form any class. The machine 
thus embodies almost all the powers of Boole’s logical 
system up to problems involving four distinct terms, and to 
represent problems of any complexity involving any number 
of terms only requires the multiplication of the parts of the 
machine. The construction involves no mechanical difficulties, 
and depends upon a peculiar arrangement of pins and levers, 
which it would not be easy to explain without drawings. In this 
arrangement of the parts the conditions of correct thinking are 
observed ; the representative rods are just as numerous as the 
laws of thought require, and no rod represents inconsistent 
attributes. The representative rods are classified, selected, or 
