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POPULAR SCIENCE REVIEW. 
copper, handmade pottery, the quaintly wrought pipes, the great plates of 
mica and lumps of galena, brought from a distance and deposited in the 
mounds, are relics which tell of a primitive people dwelling in the country 
before the Red Man got possession of the land ; but who these mound- 
builders were, whether Nahoans or Toltecs, or what not, no man at this day 
can confidently assert. Notwithstanding the multitude of relics which have 
been unearthed, we may still say of this subject, as old Camden said of quite 
another matter, 1 we walke in a mirke and mistie night of ignorance/ It 
should be remarked that Mr. MacLean not only gives a general account of 
the mounds, but includes in his book an original archaeological essay on the 
mounds of Butler County, in Ohio. 
ELECTRIC LIGHT.* 
T HE recent popularity of the Electric Light seems to have produced a 
large crop of literature on the subject, of very unequal value and 
character. The present work is stated in the Preface ‘ to contain a general 
account of the means adopted in producing Electric Light/ ‘ No attempt 
has been made to teach the science of electricity/ To this modest under- 
taking of Mr. Urquhart, Mr. Webb adds a prefatory note to the effect that 
* in revising for the press Mr. Urquhart’s little work, he has endeavoured to 
arrange the matter in accordance with the history of the subject, and to 
make a few additions on historical, theoretical, and experimental points/ 
Beyond these statements, it is not very clear in what proportion the two 
writers named on the title-page have severally contributed to the general 
result. A short introduction leads to a chapter on voltaic batteries, very 
trivial in character, at times incorrect, as, for instance, in stating that ‘ the 
dense variety of carbon known as graphite, found in gas retorts, is of 
little use and again, that i it is better to give the carbons in Bunsen batteries 
a heading of lead/ and to solder a piece of copper to the top of the platinum 
for a Grove’s battery. The author’s modification of ‘ Burnes’ negative plate 
cell ’ is stated to be 1 very portable, and may be made use of in travelling, to 
secure photographs of caves and such places/ The negative consists of a 
plate of copper, to one surface of which, as well as to its edges, a sheet of 
platinum foil, compact and free from pinholes, is soldered, and to the opposite 
surface, or back, a sheet of lead/ The exciting solution used consists of 
sulphuric acid and bichromate of potash, substances calculated to do no little 
havoc on this singular compound of platinum, lead, copper, and soft solder. 
Air is moreover pumped into the cells by means of leaden pipes, inserted in 
the liquid ! Ten of these batteries are stated 1 to produce the effects of sixty 
or seventy Grove or Bunsen cells ! ’ ‘To prevent the possibility of any dis- 
appointment in the use of this apparatus, it will be as well to tell the reader 
at once, that for every fifteen minutes or so of Electric Light, the cells will 
be nearly exhausted, and to continue at full power, ought to be refilled/ 
* Electric Eight ; its Products and Use, 8fc. By J. W. Urquhart, C.E. 
Edited by F. C. Webb, M.I.C.E., M.S.T.E., with ninety-four illustrations. 
Small 8vo. London : Crosby, Lockwood and Co. 1880. 
