Nov. 18, 1869 | 
NATURE 
85 
marking double, triple, and multiple stars, binaries (known 
or suspected), variables, Messier’s nebulz, Sir W. Herschel’s 
classification of his nebula, and so on. 
All stars in the B.A. Catalogue down to the sixth 
magnitude inclusive are to be introduced, besides all the 
objects in the Bedford Catalogue, Messier’s nebulz, about 
Too variables, red stars, and other objects of interest (in 
all about 1,500 objects). The scale of the maps is to be 
that of a 20-inch globe, and each map will be rather more 
than thirteen inches in diameter. 
Mr. Proctor’s series of gnomonic maps, in which the 
sphere is divided into the same set of pentagons, which 
are arranged into two sets of six (namely, five northern 
equatorial maps around the north polar map, and five 
southern pentagons similarly arranged around the south 
polar map) will be added as index maps. As in these 
maps the constellation figures (coloured) are introduced, 
all necessity of adding these figures to the large maps is 
avoided, and so the clearness of the maps is much 
increased. 
A letter-press introduction, with a list of star-names, 
will add to the completeness of the maps. Mr. Brothers, 
of Manchester, will photo-lithograph the maps if it should 
appear from the receipt (by him) of a sufficient number of 
names as subscribers, that the scheme is approved of 
by astronomers. He will supply to subscribers a specimen 
of Map 2, which alone is yet completed. 
LETTERS TO THE EDITOR 
[ The Editor does not hold himself responsible for opinions expressed 
by his Correspondents. | 
Personal Equation of Astronomical Observers 
CAN any of your readers inform me whether an attempt has 
hitherto been made to determine the absolute Personal Equation 
of Astronomical Observers ? The most important of all astrono- 
mical observations consists in noting the time of passage of a star 
across the wires of a transit instrument ; but it is found that no 
two observers exactly agree in the time assigned to the passage. 
From peculiar habit or bodily constitution some observers almost 
invariably register the passage of a star a fraction of a second 
before other observers. From the Introduction to the volumes 
of Greenwich Observations, we learn that it is the practice at the 
national Observatory to compare the observations of the junior 
observers with those of the principal observer, and to’ assume 
that the latter is correct. All the observations are tl us brought 
into consistency with each other ; but it is not known, I believe, 
whether all the time observations may not be a fraction of a 
second too soon or too late. . 
Cannot this question be determined experimentally in a very 
simple manner? Imagine an artificial star, formed by a minute 
| plan, and have fertilised thousands of flowers t 
| stigmatic surface, and had emitted tubes. 
electric spark, placed at a considerable distance, say three miles, 
and made to move across the field of a transit instrument at a 
rate not very different from the average apparent rate of stars 
observed (say nine inches per second): very simple mechanism 
might be devised to register upon the chronograph of the 
observatory the exact moment at which the star is absolutely 
upon each of the cross wires of the telescope. At the same time 
the observer, whose error is to be determined, should endeavour 
to record in the ordinary way the passage of the star, and the 
difference of time, as shown on the chronograph, would give the 
required error. Every observer might thus be put through a 
kind of exercise, which would inevitably show the degree of 
his proficiency, or detect any change in his habits of observation. 
I need hardly say, that however small may be the remaining 
personal error unallowed for in the Greenwich obseryations, the 
time may come when the determination of some most important 
astronomical question may depend upon that quantity. And 
though those observations may at any one time be rendered per- 
fectly consistent zzz¢er se, by reference to one observer's result, yet 
they cannot be strictly comparable with the observations of other 
observatories, or those of the same observatory at distant periods 
of time, because the one same observer would not be present to 
give the assumed standard. It might be of considerable im- 
portance, therefore, to establish a mechanical criterion of the 
accuracy of time observations which could be appealed to at any 
observatory, and at any future time. Ihave not been able to 
learn that such an experiment has hitherto been tried. 
J 
The Fertilisation of Winter-flowering Plants 
WILL you permit me to add a few words to Mr. Bemnett’s 
letter, published at p. 58 of your last number? I did not cover 
up the Zamium with a bell-glass, but with what is called by 
ladies, ‘‘net.” During the last twenty years I have followed this 
nus covered up, 
but have never perceived that, their fertility was in the least in- 
jured. I make this statement in case anyone should be induced 
to use a bell-glass, which I believe to be injurious from the 
moisture of the contained air. Nevertheless, I have occasionally 
placed flowers, which grew high up, within small wide-mouthed 
bottles, and have obtained good seed from them. With respect 
to the Vinca, I suppose that Mr. Bennett intended to express 
that pollen had actually fallen, without the aid of insects, on the 
As far as the mere 
opening of the anthers in the bud is concerned, I feel convinced 
from repeated observations that this is a most fallacious indication 
of self-fertilisation. As Mr. Bennett asks about the fertilisation 
of Grasses, I may add that Signor Delpino, of Florence, wi!l soon 
ublish some novel and very curious observations on this subject, 
of which he has given me an account in a letter, and which I am 
glad to say are far from being opposed to the very general law 
that distinct individual plants must be occasionally crossed. 
CHARLES DARWIN 
Down, Beckenham, Kent, Nov. 13 
Elimination of Alcohol 
ALLOW me to remark on a statement made in one of the 
chemical notes of last week’s NATURE. 
A new test for alcohol discovered by M. Lieben is there de- 
scribed, and its alleged value in solying an important physiolo- 
gical problem is dwelt upon. Now the real course of events has 
been as follows :—Since the year 1860, when MM. Lallemand, 
Duroy, and Perrin published their researches on alcohol and 
anzesthetics, the old belief in the combustion of alcohol within 
the organism has been almost entirely upset; and it was supposed 
that this substance was entirely eliminated without change. Dr. 
Anstie was, I believe, the first who publicly criticised the con- 
clusions of these physiologists, and showed, by a number of 
experiments, that a small proportion only of the alcohol intro- 
duced is excreted by the kidneys. [See Dr. Anstie, ‘‘ Stimulants 
and Narcotics,’ Macmillan, 1864 ; also further researches recorded 
in his Lectures on Acute Diseases at the College of Physicians, 
Lancet, 1867, vol. ii] 
The question was next taken up by Dr. Thudichum, who 
estimated the amount of alcohol excreted by a number of men 
after they had taken a considerable quantity of wine, and proved 
it to be only one-half per cent. of the total amount swallowed. 
Findlly, the writer of this, during 1866 and 1867, made numerous 
experiments in the same direction. In these, not only was it 
shown that alcohol can be detected in the urine secreted during 
