Apri 13, 1882] 
is due to the fact that there is a marked loss of electro- 
motive force in the battery. Thus the charging current 
had 91 volts, while the discharging current had only 61°5 
volts. It follows, from a consideration of the theory of 
the battery and the formula— 
_ V(E’—RT) 
I(E—RI)z 
that the efficiency must always be less than unity, but 
may be greater as the intensities and resistances are less. 
In the formula, E is the E.M.F. of the battery, R its in- 
ternal resistance, I and ¢ the intensity of the current and 
its duration during charge, while the same letters marked 
serve for the corresponding quantities during discharge. 
It is therefore advantageous to charge the battery with a 
feeble current flowing for a long time. It was observed 
also, that the resistance of the battery was lower during 
discharge than charge. 
To sum up, the charge of the battery requires a total 
mechanical work of 1°558 horse-power during 22h. 45m., 
which is equivalent to a horse-power during 35h. 26m. 
The battery only received 66 per cent. of the total work 
expended, the rest being lost in overcoming passive re- 
sistances, and exciting the field magnets. Only 60 per 
cent. of this power stored was yielded back by the bat- 
tery, and there is reason to believe that the same result 
will be forthcoming in all applications similar to lighting 
by Maxim lamps. 
THE WILD SILKS OF INDIA‘ 
HE laudable efforts of the Indian Government to 
utilise the various products of which these wild silks 
form a class will tend, by the immediate production of 
wealth, and yet more by the spirit of intercommunication 
and enterprise thus created, to overcome the great diffi- 
culty of poverty and still greater difficulty of isolation, 
which so tasked its efforts in the last famine. And this 
work is the more desirable because, as the last census 
shows, the peaceful, firm rule of the British in India has 
removed that natural check to population which was 
found of old in the mutual internecine wars of its 
peoples; and numbers have increased to such an extent 
that the failure of a crop over any wide district is 
invariably followed now by a famine. 
The principal varieties of wild silks found in India are 
the Tusser, or Tasar, the Eria, and the Muga, or Moonga, 
silks, besides several others, at present of little com- | 
mercial importance. 
Silk differs from all other materials used in textile 
fabrics in the nature of the thread as originally produced. 
Hemp, flax, cotton, wool, and many other threads are 
produced by the twisting tightly together of the short but 
very fine fibres of the raw material, the untwisting of 
which reduces the thread again to short loose fragments. 
The long fibre of the best Sea-Island cotton does not 
much exceed 14 inches in length. Silk, on the other 
hand, is spun by the silkworm (except that it is not a 
worm, and does not spin it!) in one long thread : three- 
quarters of a mile is quoted by Mr. Wardle as the length 
of the thread of a Tusser worm. There is no “spinning” 
in the process at all, but two fine threads come from 
the spinnarets of the grub as from the spinnarets of a 
spider in such a glutinous semi-liquid condition that they 
coalesce into one thread, which, in the best kind of silk- 
worms, can be wound without a break from the outside of 
the suspended cocoon to where the grub left off spinning 
and turned into a chrysalis. The silk-reeler does not, 
even in the coarse Tusser variety, ree] off a cocoon of this 
singly, but from four to six together, whose gummy 
surfaces make them combine into a single thread still 
fine. 
4 “Handbook of the Collection Illustrative of the Wild Silks of India in 
the Indian Section of the South Kensington Museum,” by Thomas Wardle. 
(Eyre and Spottiswoode, 1881.) 
NATURE 
563 
The Eria cocoon is not found practically so available 
for this treatment, but, in addition to the beautiful con- 
tinuous thread of the Bombyx or Tusser silkworm, the 
waste part of their cocoons can be treated like the 
vegetable fibres (cotton, &c.) of which we spoke with 
equally good results as a textile material, and with nearly 
all the beauty of the perfect silk thread. For this pur- 
pose the whole of the cocoon of the Eria is specially 
available, and, instead of being carefully reeled off, it is 
cut up or torn into shreds by the carding machine, and 
then treated as a long staple cotton. This is known as 
spun silk, or by the more recent name of Schappe. If, 
however, the surface of such a thread is examined, even 
with small magnifying power, it will show the loose ends 
of the fibres sticking out in every direction ; and although 
they are individually too fine to attract the attention of 
the naked eye, in combination they are quite patent to the 
finger and to the ear, a soft deadness resulting instead of 
the sharp whistle of the natural silk, on which are no 
fibres except the ends left by careless throwsters. 
Another inferiority of spun silk, though not a great one 
in the ever-changing fashionable world of England, is 
that it has not the durability which distinguishes the 
continuous silk thread. Yet in India garments made from 
the former are handed down from mother to daughter ! 
The Tusser or Tusseh larva, whose coarse, strong 
thread is available for thrown silk, is a monster compared 
with the larva of the Bombyx mori, or common silk-worm, 
It measures 7 inches in length and 1 inch in diameter; 
the wings of the moth—a very handsome one—are 7 
inches across, and the thread also is three times as coarse, 
and three times as strong as that of the China silkworm. 
Here, however, comes an objection to it in the eye of the 
manufacturer. While the thread of the Bombyx is almost 
round, the extra coarseness of the Tusser thread all con- 
sists in its extra width : it is, in fact, three times as broad 
asit is thick. Like any thread of this shape compared 
with a round one, it has a great tendency to split, and 
consequently become rough in working. Another diffi- 
culty to both reelers and dyers is caused by the substan- 
tial way in which the Tusser grub forms its cocoons. 
Major Coussmaker observes that— 
‘“ As the chrysalis remains in the cocoon as long as eight 
months, exposed to the hottest sun and occasional thunder- 
storms, the cocoon had need to be made a hard impene- 
trable material; so indestructible is it, that Bheels and other 
tribes which live in the jungles, use the cocoon as an ex- 
tinguisher to the bamboo tube in which they keep the 
‘falita’ or cotton tinder used by them for lighting their 
tobacco and the slow matches of their matchlocks. The 
cocoon is also cut into a long spiral band, and used for 
binding the barrel of matchlocks to the stocks, being, as 
the natives say, unaffected either by fire or water..... 
After the caterpillar has spun a layer of silk thick enough 
to conceal itself, it discharges some kind of gum or 
cement, thick like plaster of Paris, and with its muscular 
action it causes this secretion to thoroughly permeate the 
whole cocoon and solidify the wall. In this manner it 
goes on spinning layer after layer of loops, and cementing 
them altogether until the whole of its silk is exhausted, 
and the wall of the cocoon becomes so hard that it 
requires a sharp penknife to cut through it’’ (pp. 18, 19). 
Again, in a later report (February 21, 1880), Major 
Coussmaker writes ; — 
“One of the most interesting, and I think important, 
facts that I have this year been able to prove, is with 
regard to the composition of the cement with which the 
caterpillar hardens its cocoon. Former analyses of this 
agent made for me, in England by Dr. Taylor, and in 
Bombay by Dr. Lyon, had shown that it contained the 
acid urate of ammonia, that it was in fact excrementitious ; 
and this year, by opening the cocoons at various intervals, 
I was able to convince myself of the fact that when the 
caterpillar has left off feeding and begins to spin, it voids 
