SCIENCE. 
19 
An exhibition is now in progress at Clarendon Hall, 
New York City, of a Dr. Tanner, who claims to be ex- 
isting without any nourishment, but that derived from 
rinsing his mouth occasionally with cold water. At 
the date of our seeing Dr. Tanner, eight days of such 
fasting were supposed to have been carried out. The 
fact that Dr. Tanner has declined those rigid conditions 
prescribed by Dr. William A. Hammond, which would 
have made fraud impossible, and is watched merely by 
persons of his own selection, deprives the so-called ex- 
periment of scientific interest. Under these circumstances 
a judgment of the case is impossible ; but a critical ob- 
servation of Dr. Tanner and his surroundings was very 
unfavorable to the genuineness of the proceedings. Dur- 
ing the fifteen minutes we remained, two opportunities 
were presented for Dr. Tanner to take food unobserved 
by his watchers — once when he ordered the light to be 
removed, and the room was made sufficiently dark to 
obscure his movements ; and again when Dr. Tanner 
left the room and reclined on the top of the portico ; dur- 
ing this time the watchers were in another room, and had 
we been confederates of Dr. Tanner, we could have 
handed him food unobserved. 
We are informed that the Earl of Rosse dseires the 
services of an Assistant Astronomer tor his well-known 
Observatory. The address of Lord Rosse is Birr Castle, 
Parsonstown, Ireland. 
On the shores of the Lake of Constance the rare 
phenomenon of a perfect solar halo was noticed on May 
4, at noon. The large ring, which from time to time 
assumed splendid rainbow tints, remained visible for 
more than two hours. At Berlin the phenomenon of 
mock suns was observed on the 9th inst., at 8 a.m. 
The Proceedings of the Davenport Academy of Natural 
Sciences, while it contains a number of papers in natural 
history, is noteworthy mainly for the large number of 
papers on subjects connected with American ethnology, 
and chiefly on various mound explorations. We are 
pleased to see that this society continues to prosper. It 
had the originality to elect as its president for 1879 Mrs. 
Mary L. D. Putnam. 
In the Transactions of the Academy of Science of St. 
Louis are several papers deserving attention. Mr. N. 
Holmes has a specially interesting paper on the “ Geolog- 
ical and Geographical Distribution of the Human Race,” 
and students of the science of language will be interested 
in M. Coruna y Colludo’s account of the Zoque language, 
spoken in the State of Chiapas, Mexico. There are two 
magnetic papers by Prof. Nipher ; a paper on Peniremites 
by Dr. G. Hanbach ; on the genus Pinus by M. G. En- 
glemann, who has also a short paper on Acorns and 
their Germination. 
Mr. C. S. Sargent, Harvard Professor of Arboriculture, 
has published, in his capacity of Speeal Agent of the ap- 
proaching United States Census, a “Catalogue of the 
Forest Trees of North America,” preliminary to one 
which will be added to the census report on the forest 
wealth of the United States. He desires information 
concerning the geographical range of any species ; the 
most favorable region and elevation and geographical 
formation for its multiplication and perfection ; its excep- 
tionally large dimensions ; its common or local name ; 
and its products and uses. 
Professor C. G. Rockwood, of Princeton, who has for 
some time devoted his attention to the study of earth- 
quakes and volcanic phenomena, desires to come into 
communication with other workers in the field of Seis- 
mology, either at home or abroad. He is especially de- 
sirous to obtain correspondents upon the Pacific Coast, 
who wpuld aid in collecting information in regard to 
earthquake shocks in that region, where they are so 
much more frequent than on the Atlantic seaboard. 
Professor C. W. Fuchs, formerly of Heidelberg, but now 
of Merin, Tyrol, Austria, has for the last fifteen years 
published annual statistics of earthquakes, and as it is 
clear from these lists, that but few cases of such phenom- 
ena in America are noted, we trust our readers will re- 
spond to the present request of Professor Rockwood. 
FARADAY’S OBSERVATIONS ON SILVERING 
GLASS. 
1,540 grains of nitrate of silver being treated with 955 
grains of strong solution of ammonia, and afterwards with 
7,700 grains of water, yields a solution to which, when clear, 
170 grains of tartaric acid, dissolved in 680 grains of water, 
is to be added, and then 152 cubic inches more of water, 
with good agitation. When the liquid has settled, the clear 
part is to be poured off; 152 cubic inches of water to be 
added to the remaining solid matter, that as much may be 
dissolved as possible; and the clear fluids to be put together 
and increased by the further addition of 61 cubic inches of 
water. This is the silvering solution. No. 1. A second 
fluid, No. 2, is to be prepared in like manner, with this dif- 
ference, that the tartaric acid is to be doubled in quantity. 
The apparatus employed for the silvering of glass plate con- 
sists of a cast iron table box, containing water within, and 
a set of gas burners beneath to heat it ; the upper surface of 
the table is planed, and set truly horizontal by a level and 
covered by a varnished cloth ; heat is applied until the tem- 
perature is 140 deg. Fah. The glass is well cleaned, first 
with a cloth ; after which a plug of cotton, dipped in the 
silvering fluid and a little polishing powder, is carefully 
passed over the surface to be silvered, and when this appli- 
cation is dry it is removed by another plug of cotton, and the 
plate is perfectly clean. The glass is then laid on the table, 
a portion of the silvering fluid poured on to the surface, and 
this spread carefully over every part by a cylinder of india- 
rubber stretched upon wood which has previously been 
cleaned and wetted with the solution ; in this manner a 
perfect wetting of the service is obtained, and all air bub- 
bles, &c., are removed. Then more fluid is poured on to 
the glass, until it is covered with a layer about the one-tenth 
of an inch in depth, which easily stands upon it, and in that 
state its temperature is allowed to rise. In about ten 
minutes or more silver begins to deposit on the glass, and 
in fifteen or twenty minutes a uniform opaque coat, having 
a greyish tint on the upper surface, is deposited. After a 
certain time the glass employed in the illustration was 
pushed to the edge of the table, was tilted that the fluid 
might be poured off, then washed with water, and examined. 
The under surface presented a perfectly brilliant metallic 
plate of high reflective power, as high as silver can attain to ; 
and the coat of silver, though thin, was so strong as to bear 
handling, and so firm as to stand polishing on the back to 
any degree, by rubbing with the hand and polishing powder. 
The usual course in practice, however, is— when the first 
stratum of fluid is exhausted — to remove it, and apply a 
layer of No. 2 solution ; and when that has been removed, 
and the glass washed and dried, to cover the back surface 
with a protective coat of black varnish. When the form of 
the glass varies, simple expedients are employed, and by 
their means either concave, convex, or corrugated surfaces 
are silvered, and bottles and vases coated internally. It is 
easy to repair an injury in the silvering of a plate. 
The advantages are — the production of a perfect reflecting 
surface; the ability to repair; the mercantile economy of 
the process (the silver in a square yard of surface being 
worth only is 8d) ; the certainty, simplicity, and quickness 
of the operation ; and, above all, the non-employment of 
mercury. 
