Fuly 9, 1885] 
NATURE 
225 
the most prominent teaching establishment in the world. 
There is not a single point of interest connected with the 
cropping and manuring of the land, the forming and 
treatment of pastures, and the feeding of animals, which 
has not been made the subject of exhaustive experiment 
at Rothamsted, while the silo experiments which have 
been lately undertaken for the purpose of testing the 
value of ensilage, will probably do more for the instruc- 
tion of those land-proprietors and large farmers who are 
watching them than all else which has been said or done 
in regard to this much-praised cattle food. It would be 
strange indeed if agriculturists refused to listen to Sir 
John Lawes, but although certain facts of prime import- 
ance in the long catalogue of useful lessons from 
Rothamsted have been widely distributed, the voluminous 
writings of the great experimenter, trusted as he is, are 
not read by one per cent. of those on whose behalf they 
were undertaken. Some of the more important teachings 
of Rothamsted have become so familiar that they have 
passed into agricultural axioms, such as “ phosphorus for | 
turnips, nitrogen for corn.” We have ourselves known 
farmers who have travelled a hundred miles—a long 
flight for such men—for the purpose of seeing for them- 
selves at Rothamsted how corn might be grown continu- 
ously by means of small dressings of nitrogenous manures, 
and thus they have solved a problem of vital importance 
to themselves and their families. But comparatively few 
farmers will trust themselves so far from home, even ona 
matter of life and death, and it has become a business of 
grave importance to the rent-receiving portion of the 
landed interest to convey to the rank and file of tenant 
farmers the necessary knowledge which they are too 
inert and ignorant to acquire for themselves. 
In the hope of teaching farmers, the Royal Agricultural 
Society, the Bath and West of England Society, some 
landlords in Sussex, and others, are endeavouring to in- 
crease the number of experimental farms. Minds that 
are entirely untrained or ignorant can only be taught 
orally or by imitation. Put an attractive story into the 
hands of an ill-instructed boy, and he will soon lay the 
book aside ; but, read or relate the story to him, and he 
will probably be found a fascinated listener. It is the 
same with farmers and scientific farming. They cannot 
learn from books, but they will listen to the story by word 
ef mouth. The leading agricultural societies are therefore 
making a timely move in considering the best methods of 
teaching farmers by example—that is, by the multiplica- 
tion of experimental farms. Lectures delivered by pro- 
fessors, and listened to with stubborn incredulity, are of 
little use compared with experiments tried by the road- 
side and discussed at the market tables of the neighbour- 
hood. It is gratifying to notice, therefore, that at a 
recent Council meeting of the Royal Agricultural Society 
a new departure was announced in the appointment of a 
committee to consider how the National Society could 
best co-operate with local societies in carrying out in- 
vestigations into subjects of practical utility in agriculture. 
An additional reason for multiplying stations is that, in 
consequence of the variation of climate and other causes, 
farming is conducted under different conditions in the 
several districts. In one locality, for example, the special 
problem to be solved may concern the management of 
grasses, in another that of corn. In all alike the object of 
the teachers of agriculture must be to substitute, so far 
as may be possible, the rule of three for the rule of thumb 
at present in vogue. 
At Rothamsted the experiments of the past forty years 
have related to the growth of continuous crops year after 
year on the same land, to the growth of crops under rota- 
tion, to the use of every kind of artificial manure, or of 
farm-yard dung, in varying quantities on every kind of 
crop, and, for the sake of comparison, to the omission of 
all manure on some of the land, to the manuring of -per- 
manent pasture, fallowing, the use of various feeding 
stuffs, town sewage, the question whether plants assimilate 
free nitrogen, ensilage, rainfall, and the waste of nitrogen in 
land-drainage water. It has been stated that some of the 
elaborate investigations which have been conducted at 
Rothamsted are too “scientific” for humbler establish- 
ments. If by science we mean a complete knowledge of 
facts the phrase is hardly accurate, but no doubt some of 
the Rothamsted experiments were accompanied by the 
analyses of animals, plants, and soils, and could not 
therefore be repeated at ordinary stations. On the other 
hand, the most useful experiments for the instruction of 
farmers are those which relate to the effects of the 
different foods employed for plants and animals, and in 
these cases farmers can themselves form estimates of the 
results which will prove sufficiently accurate for practical 
purposes and may lead to the saving of millions which are 
now annually wasted through the ignorant use of manures 
and improper feeding of animals. BoE 
ELECTRICITY AT THE INVENTIONS 
EXHIBITION 
The Secondary Generators of Messrs. Gaulard and Gibbs 
ITHERTO there have been two means employed 
for electric illumination and the electric transmission 
of energy—viz. supplying the electricity required for the 
lamps or other receivers (1) direct from the dynamo 
machines, and (2) from secondary batteries charged by 
means of dynamos. A third method has been recently 
introduced, by means of secondary generators, of which a 
small installation has been made at the Inventions Exhi- 
bition, to which we propose to refer in this article. 
The object of this invention is to supply a current 
which may be varied at will both as regards electromotive 
force and quantity, and thus be made applicable to work 
at the same time arc lamps, incandescent lamps, and 
motors. The means by which this result has been 
effected is by interposing between the dynamo machine 
and the lamp or other receiver of electricity a supple- 
mentary apparatus, by the use of which an induced 
current is produced proper to the particular receiver 
which it is desired to work. 
The National Company for the Distribution of Elec- 
tricity by Secondary Generators, which works the patents 
of Messrs. Gaulard and Gibks, originally used secondary 
generators of the following construction. They were 
composed of a thick insulated copper wire, surrounded 
by smaller coils formed of a number of thin insulated 
copper wires ; the thick central wire receiving the current 
from the dynamo, which was distributed through the 
secondary wires. This method of construction has been 
replaced by one of exceeding simplicity, in which the 
difficulty of insulation and complication of manufacture 
of the original form are done away with. 
The conductor for the primary current and the con- 
ductor in which the induced current is produced consist 
of a series of annular disks of sheet copper } millimetre 
in thickness and 3} centimetres in width, slit across at 
one part and furnished with projecting pieces extending 
outwards on either side of the slit. The conductor for 
the primary circuit is made up of a series of these annular 
disks, and the conductor for the induced current is made 
up of a second similar series, the two series being so 
interlaced that the convolutions of the helix formed by 
the disks for the primary circuit alternate with the con- 
volutions of the helix formed by the disks of the induced 
circuit. An annular disk of insulating material, such as 
paratfined cardboard, is placed between each convolution 
of the double helix thus formed, so as to prevent short 
circuiting between the helices and the several convolu- 
tions thereof, and the projecting pieces of all the disks 
for the primary current are soldered or electrically con- 
nected together, and the projecting pieces of all the disks 
