Dec. 28, 1882] 
NATURE 
205 
collateral testimony to subsequent observations pointing 
in the same direction. To say nothing of other authorities, 
the accurate designs of the deeply-regretted Burton, and 
the latest delineations of Schiaparelli (independent of the 
wonderful duplication of the narrow streaks) concur with 
the drawings of Schréter in indicating one of two suppo- 
sitions as regards the dark patches of Mars; either they 
must be liable to long-persistent and very deceptive 
alteration of visible outline from atmospheric causes, or: 
their own extent must be so variable as to awaken a doubt 
whether the right key of the mystery is after all in our 
hands. We have long believed that we hold it, and ter- 
restrial analogy has been thought sufficient to account for 
all we can see. The result of the next opposition in 
1884 may be found to confirm the old hypothesis ; but it is 
not beyond possibility that it may shake it, even past 
recovery. 
Besides the conclusion thus briefly indicated, several 
other points of varying degrees of interest are touched 
upon in this comparatively bulky treatise, some of 
which we may refer to, though only with a_ passing 
notice. Schr6ter paid considerable attention to the polar 
whiteness; but while he admits the probable analogy of 
terrestrial snow, he is less confident than some other ob- 
servers as to any marked influence of solar radiation. 
Terby, however, has pointed out the cause of his misap- 
prehension, and his substantial agreement with his com- 
peers. He was aware of the irregular outline of the 
snowy regions, and thought them slightly different in 
colour, the south pole verging towards yellow, the north 
blue. On the question of rotation he could obtain no 
satisfactory result, as might have been expected from his 
idea as to the instability of the markings ; his values 
being discordant at different periods: the mean, 
24h. 39m. 50°2s., was only about 29s. less than that of 
Sir W. Herschel, but very wide of Proctor’s elaborately 
deduced value, 24h. 37m. 22°735s.—a fact pointing pro- 
bably to the same conclusion as before, that from some 
as yet imperfectly explained cause, the exact position in 
longitude of some of the features of the planet is not 
fully ascertained. The amount of the polar flattening of 
Mars is, as is well known, matter of much uncertainty. 
Herschel made it as much 1-16 ; Dawes, nothing, or even 
negative. Our observer, nearest to the great English 
authority, found it less than 1-81, a quantity fairly evan- 
escent. The method of measurement which he adopted 
throughout all his researches was that of the apparatus 
which he calls the “ projection machine.” 
In this simple 
contrivance both eyes are employed simultaneously, the 
one in viewing the telescopic image, the other in bring- 
ing to coincidence with it, a squared-out area in the case | 
of the moon, a series of discs for the planets, in either | 
instance with provision for varying distance and illumin- | 
This binocular mode of measurement, if open to | 
some sources of error not incidental to the ordinary | 
ation. 
apparatus, appears hardly deserving of the censure so 
freely bestowed upon it by Beer and Madler, who were 
not always fair towards the labours of Schréter; and 
notwithstanding the perfection to which the wire micro- 
meter has been brought, might perhaps be revived for 
some purposes with advantage. The diameter of Mars 
obtained in this way by Schrdéter, 9°84, does not differ 
much from the 9” 8” (a curious instance, by the way, of 
notation by ¢hzrds), of Sir W. Herschel, or from more 
modern values—some proof, it may be thought, of the 
competency of the apparatus to obtain a close approxi- 
mation. 
Observations included in this volume of a partial 
flattening of the limb of Mars and of the abnormal | 
breadth and want of symmetry in the phasis, however 
improbable they may at first appear, are not without 
parallel in the case of other planets, or the experience of | 
If, as it must be assumed, these are | 
other observers. 
nothing more than illusions, the record of them is still 
valuable in the probable event of their occasional re- 
currence. 
To this brief and imperfect notice are appended three 
sketches from the Atlas—the two first as specimens of 
Schréter’s mode of delineation—the third as bearing so 
striking a resemblance to one of my own, shown on a 
smaller scale beside it, that it might, in the absence of 
more accurate data, serve as the basis of an approximate 
value of rotation. 
The dates respectively corresponding to these designs 
are 1798, Sept. 9d. 8h. 4m.; Oct. 17d. 7h. 39m.; Nov. 
13d. 7h. tom. ; 1862, Dec. 1od. 9d. 30m. 
T. W. WEBB 
DESTRUCTION OF LIFE IN INDIA BY 
POISONOUS SNAKES 
ji January, 1870, being then in Calcutta, I collected 
statistical information which afforded proof that the 
loss of human as well as animal life in India from the 
bite of venomous snakes was very great; and as it 
seemed to me that this ought to be, to a great extent, 
preventible, I extended my investigations with the view 
of obtaining accurate information as to the characters 
and peculiarities of the venomous snakes themselves, the 
localities in which they most abound ; the modus operandz 
