162 
NATURE 
[ DECEMBER 17, 1903 
object for which it was installed, which was to determine 
““the times at which various phases of motion are recorded ”’ 
(see British Association Reports, 1897, p. 130. Copy of a 
circular sent to foreign Governments and colonies). This 
it does, and a little more. If an observer desires to have 
an open diagram, he must employ clockwork to drive the 
record receiving surface at a higher speed, whilst a longer 
period than the one usually employed can be obtained by 
adjustment. It must, however, be remembered that the 
period obtained at one station may, on account of the 
wandering of the pendulum and “‘ tremors,”’ be unpractical 
at another, and that difference in adjustment at different 
stations destroys uniformity. Although with the object of 
stimulating further research we have criticised certain 
portions of the work before us, the bulk of it commands the 
admiration and thanks of all seismologists. 
THE GILBERT TERCENTENARY. 
HE tenth of this month was the three hundredth anni- 
versary of the death of Dr. William Gilbert, the cele- 
brated Elizabethan philosopher who laid the foundations of 
the science of electricity. The occasion was celebrated on 
Thursday, December 10, at the meeting of the Institution 
of Electrical Engineers by the presentation of a picture by 
the Institution to the town of Colchester, in which place 
Gilbert was born and died. The picture was painted by 
Mr. Ackland Hood; it is a fine historical painting repre- 
senting Dr. Gilbert showing his electrical experiments to 
Queen Elizabeth. 
The proceedings were opened by the president of the 
Institution with a short speech. Prof. S. P. Thompson 
then gave a brief address, in which he outlined Gilbert's 
life and his contributions to science. Gilbert was born in 
Colchester in 1544, and was educated at the school there 
and subsequently at St. John’s College, Cambridge, at 
which he became mathematical examiner and senior bursar. 
He took the degree of M.D. in 1569, and rapidly advanced 
in the profession, becoming in 1599 president of the Royal 
College of Physicians, and a year later physician to the 
Queen. He died at Colchester on December 10, 1603, and 
was buried there in the Church of Holy Trinity. Eminent 
as he was as a physician, his claim to immortality rests 
not on his work in medicine, but on his pioneering investi- 
gation in the then almost non-existing sciences of magnetism 
and electricity. To him we owe the science of terrestrial 
magnetism ; by numerous and careful experiments upon the 
loadstone he discovered many of the most important prin- 
ciples of magnetism, such as the existence of a magnetic 
field—an “‘ orbe of virtue ’’—around the magnet, the screen- 
ing effect of iron, and the destroying effect of heat. From 
experiments on a globular loadstone he was able to evolve 
the theory that the earth is itself a great magnet. Thus 
many years before Bacon, who is usually regarded as the 
father of the inductive method, Gilbert was using this 
method with signal success. 
Gilbert’s contributions to electricity are contained in the 
second chapter of Book ii. of the celebrated ‘‘ De Magnete.”’ 
He showed that not amber alone, but many othenubodies 
which he put in a class called electrics, can attract solid 
bodies when rubbed; that they attract everything, not 
merely straws or chaff; that damp weather hinders the 
electrification ; and that a flame destroys it, as well as many 
other important facts which are now the fundamental prin- 
ciples of the science. He invented the electroscope, and 
discovered that the force of attraction is in a straight line 
towards the electrified body. From these simple beginnings 
has been gradually evolved in 300 years the immense 
structure of pure and applied electricity. 
The Mayor of Colchester thanked the Institution for its 
gift in a brief and humorous speech. Amongst many other 
distinguished men present at the meeting were Sir W. 
Huggins, president of the Royal Society: Sir Dyce Duck- 
worth, treasurer of the Royal College of Physicians, an 
office twice held by Dr. Gilbert; Prof. J. Larmor, represent- 
ing St. John’s College, Cambridge; the Mayor of West- 
minster; and Mr. Ackland Hood, the painter of the 
picture, 
NO. 1781, VOL. 69] 
AGRICULTURAL NOTES. 
“THE third report on the Woburn Experimental Fruit 
Farm, recently issued by the Duke of Bedford and Mr. 
Spencer Pickering, F.R.S., is devoted to a discussion of 
the effects of grass on apple trees. In previous reports it 
was shown that grasses prove most injurious to young 
apple trees, and the experiments described here were de- 
signed to throw light on the causes of injury. Up to the 
present time the cause, or causes, have not been discovered, 
but the experimenters have made considerable progress, for 
they have shown that their first suspicions were unfounded. 
Grasses might reasonably be expected to injure young fruit 
trees by interfering with their air, or water, or food supply, 
but the careful experiments recorded in the report indicate 
that interference with air, water, and food has little or 
nothing to do with the question, and that the injury ‘‘ must, 
in all probability, be attributed to the action of some pro- 
duct, direct or indirect, of grass growth which exercises an 
actively poisonous effect on the roots of the tree.’’ This 
conclusion is based partly on the negative evidence of the 
experiments, in which the supplies of food, air, and water 
were controlled, and partly on the appearance of the trees 
grown in grass. These trees were always very sharply 
marked off from the others by peculiar tints of leaf and 
fruit, quite unlike those due to starvation, and produced 
obviously by some unhealthy condition of soil. The effects 
of grass on apple trees: have been studied only on the 
shallow clay soil of the Woburn Fruit Farm and on a clay 
soil at Harpenden, and it is possible, as the experimenters 
are careful to point out, that on a richer soil, and in a 
different climate, grass might not prove injurious, but the 
Woburn experiments clearly indicate that horticulturists 
should avoid planting apples in grass, unless there is 
local evidence that grass does not injure the young trees. 
In their work on apple trees the Duke of Bedford and Mr. 
Pickering are dealing with a special and well-marked case 
of a general problem of great interest to agriculturists— 
the effects of crops and of crop residues on the quality of 
soil. Every observant cultivator knows that land may get 
““sick ’’ or ‘‘ over-cropped’’ when a plant is grown too 
often, and he also finds that certain plants ‘‘ exhaust ’’ the 
soil in a peculiar degree for certain other plants. He has 
been told that this is a ‘“‘ food ’’ or a ‘* special food ”’ ques 
tion, and that interference with the air, food, and water 
supply explains all the ills which plants may suffer from 
competition with their fellows. At the same time, he does 
not feel satisfied that such phenomena as the disappearance 
of clover from land, or the effects of rye-grass on wheat 
are due to straightforward competition, and the ‘* poison ’” 
theory of the Woburn experimenters will arrest his atten- 
tion. Seventy years ago agriculturists were discussing 
De Candolle’s ‘‘ excretory theory,’’ and found in it the chief 
explanation of the benefits due to a rotation of crops; when 
the theory was abandoned the facts from which it originated 
were forgotten, and in connection with the effects of grass 
roots on apple trees the following sentence from De Can- 
dolle is worth recalling :—‘‘ Thus we know that the 
thistle is injurious to oats, the Euphorbia and Scabiosa to 
flax, the Inula betulina to the carrot, the Erigeron acre and 
tares to wheat, &c.’’ Though the plant does not ‘‘ excrete,’” 
it may readily influence the character and condition of the 
soil either directly by the decomposition of its roots, or 
indirectly through its effect on soil organisms, and the 
Woburn experiments, which deal with this subject, will be 
closely followed. 
In a paper entitled ‘‘ Recherches sur la Synthése des Sub- 
stances Albuminoides par les Végétaux,’’? MM. Laurent and 
Marchal, of the State Agricultural Institute, Gembloux, 
give a useful résumé of the sources of nitrogen to plants. 
In doing so they point out that during the latter half of 
the nineteenth century there was a tendency to overlook 
the importance of ammoniacal compounds, and to regard 
nitrates as the only sources of nitrogen to the higher 
plants. While nitrates are of chief importance, there are 
many plants, even colonies of plants, such as forest trees. 
and the vegetation of marshes, that must depend largely or 
entirely on compounds of ammonia for the supply of 
nitrogen. The authors describe experiments on cress, white 
mustard, chicory, asparagus, white melilot, Persian lilac, 
and tobacco, and among other conclusions state that sun- 
a 
