602 
especially in two directions, as all the world knows, suc- 
cess was complete. By the use of the wedge photometer, 
Pritchard raised stellar photometry to the dignity of an 
exact science, and by the employment of photographic 
methods he investigated the parallaxes of a large number 
of stars with results which are probably among the most 
trustworthy ever obtained in this branch of astronomy. 
Another epoch in Pritchard’s astronomical career com- 
menced with his offer to take part in the work of the 
international photographic star chart. Such an under- 
taking, at his advanced age, was characteristic of him ; 
and the fact that he successfully initiated the work, and 
left everything in order at the time of his death, illustrates 
the methodical way in which he set about it. 
The successful issue of the various undertakings at 
Oxford was largely due, as Pritchard himself was always 
anxious should be known, to the zeal of his assistants, 
Messrs. Plummer and Jenkins, by whom most of the 
actual observations were made. 
Prof. Turner has succeeded in weaving together an 
admirable account of Pritchard’s astronomical work, but 
it may be remarked that all reference to his connection 
with the work of the Committee on Solar Physics has 
been omitted. 
A hitherto unpublished account of Pritchard’s observa- 
tions of the total solar eclipse of 1860 is included in Prof. 
Turner’s story, and though these were overshadowed by 
De la Rue’s magnificent photographic results, it is evident 
that they were carried out with the forethought and skill 
which marked all his work. 
The selection of correspondence between Pritchard 
and some of his great contemporaries has, on the whole, 
been judiciously made, and all concerned in the prepara- 
tion of the memoirs are to be congratulated on the 
production of a volume which will be prized by all 
who knew Pritchard, and one which is at the same time 
of sufficient interest to command the attention of a much 
wider public. 
WATER AND ITS PURIFICATION. 
Water and its Purification. By Samuel Rideal, D.Sc. 
Pp. xii + 292. (London: Crosby Lockwood and Son, 
1897.) 
HE author of this work describes it on the title-page 
as “a handbook for the use of local authorities, 
sanitary officers, and others interested in water supply.” 
It is thus admittedly a book which is designed more for 
the general reader than for the engineer, the chemist, or 
the bacteriologist. That this is so we have further 
evidence in the preface, where we read that— 
“The closing of polluted wells, and decisions on new 
supplies, are now, however, in the hands of the general 
public, who, and their elected representatives, thus need 
to become acquainted with the results of the progress 
made during the last few years in bacteriology and 
knowledge of the causation of disease.” 
The book deals with the characters of different kinds 
of natural water, animal and vegetable impurities, the 
storage, filtration and distribution of water, the softening 
and purification of water, and lastly its analysis and the 
interpretation of results. On reading the book one finds 
that the author has not been able to refrain from in- 
cluding a large amount of technical detail, which is, 
NO. 1435, VOL. 55] 
ead URE 
however, treated too superficially to be useful to the 
serious student of the subject, and which must be of 
little or no use to the general reader. One cannot help 
wondering, for example, what sort of hazy notion the 
general reader will obtain from Figs. 614-63, which show 
a colony of typhoid bacilli, and the typhoid bacilli them- 
selves with and without flagella, the former called 
“spider” forms. The author is careful to inform the 
reader, on p. 266, that “the séze of organisms is recorded 
in micro-millimetres = 7 oly9th of a millimetre commonly 
abbreviated pw", but avoids recording either the size of 
organisms which are figured in the book, or the magni- 
fication to which they have been subjected, except in 
one case where the magnification happens to have been 
included in the descriptive letter-press copied with the 
figure from another book. 
It is equally objectionable to place together in one 
plate, objects requiring differing degrees of magnification, 
as in Fig. 13, which exhibits in a single view a gigantic 
cyclops, spores of moulds, a zoogleea mass of bacteria, 
&c. Such figures may be well suited for advertisements 
of filters in order to show up the horrors of drinking 
water aw naturel, but must prove somewhat misleading 
to the reader who obtains his first ideas of such objects 
from this book. On p. 256 the reader is informed that 
the flagella of bacteria “should be looked for by careful 
staining with iodine, fuchsine or other reagent.” It 
would be advisable for any one who wishes to see these 
curious appendages of bacteria to select the ‘other 
reagent” referred to, for the employment of those named 
would be quite inadequate for his purpose. On p. 257 the 
author falls into the common error of supposing that 
aerobic organisms “are incapable of existing in absence 
of air”; as a matter of fact, when deprived of free oxygen 
they can lie dormant for very long periods of time, and 
wait for its advent as a signal for the renewal of their 
activity. 
It is a little curious that an author who desires to 
inform his readers on such up-to-date topics as the 
staining of the flagella of bacteria, “spider-forms” of 
typhoid bacilli, and the latest methods of examining a 
sample of water for typhoid and cholera, should lay such 
stress on the history and properties of “the divining- 
rod.’ In the midst of a very useful résumé of facts 
bearing on the movements of water in various strata, on 
subsoil-water, line of saturation, “faults” and artesian 
wells, the author offers the following rather startling 
advice to the “local authorities and others” who may 
be in search of underground water. Instead of advising 
them to consult an engineer or geologist, as one would 
expect from the geological treatment of this part of his 
subject, we read on p. 77— 
“Tt is worth while for any one who has occasion to 
seek for underground water, before going to the expense 
of boring, to employ /rs¢ (the italics are the author’s) a 
‘ water-finder,’ and at the same time to invite a scientific 
authority to test the process in detail without bias, as 
the practical success seems sufficient, if not to shadow a 
new law, like the discovery of the Roéntgen rays, yet by 
explanation to put this peculiar power in a position 
where it could be more largely useful and less hesitatingly 
accepted.” 
From the account given of a certain experiment with 
the divining-rod, the unknown power seems to act even 
