46 0. C. Marsh on a new species of Protichnites. 
ing observation, first made by Mr. Schultz, that in very rich 
cannel g: as, there is actualy an increase of intensity within 
certain iimits due to the presence of oxygen, suggests another 
series of experiments with successive additions of oxygen to a 
gas of high illuminating power, which we propose to under- 
take at our early convenience, as also another series upon mix- 
tures of progressive quantities of carbonic acid, 
May 17, 1869. 
Nots.—Erdmann's Photometer (‘ Gaspriifer”) depends on the use of air to de- 
stro ey illuminating power of gas. El ster has e mployed t this s instrument in a 
gas. If 
of 1 per cent of Lsjeane gas to the decarburetted gas employed in a defini 
burner, is calle e candle, 0 ee found necessary to add 6°5 per cent of air to 
destroy the illuminating power of this gas containing one per cent of olefiant 
carbonic acid, we may eg an ordinary 12-can sinh se a mixture of a 
known non-luminous gas, holdin irae in suspension during combustion a quantity ra 
, equivalent to 12 as cent ed olefiant pi and requiring, conse- 
que ntly, a quantity of air equal to volumes for 100 volumes of gas 88X15 
+12X65=210). Each additional cand ‘heraet requires an addition of 5 vol- 
umes of air, as the constant indicated by these results of Elster. cies: lated 
In the use of the ann apparatus, it is rise oe vo volume of air 
quired completely to destroy the illuminating pow al-gas ranges fice 188 
to 245 volumes 4 on volumes of gas, adda with te sides ess 
These results, it will be obser yee harmonize in a satisfactory manner with 
those obtained by Pp as embodied in Table L 
Every ¢ weiey ist will at once recuy, also, to the action of air upon gas in the 
Bunsen burner, in constant use in all laboratories provided with gas—an instru- 
ment identical 4 in principle with the Gaspriifer of Erdmann 
Art. V.—Description of a new Species of Protichnites from 
the Potsdam Sandstone of New York; by QO. C. Marsh, Pro- 
fessor of Paleontology in Yale College. = (Witha plate. ) 
Tue first discovery of footprints in the Lower Silurian of q 
this country appears to have been made in 1847, in the Pots- — 
dam sandstone at Beauharnois, Canada East. In 1851 an ac- 
pacers of the pa ges thes ublished by Sir Wm. E, Logan, and — 
th it ap gag short « ah tion of the impressions them- 
selves by Prof. Owen, of on, who then considered them 
tracks of a Tortoise.} Subsequent explorations by the Geolog- 
ical Survey of Canad So t to light new localities and ad- 
ditional specimens in the same region, and in the following year 
* before the Am. ion of Science, Mee Au 1868, 
+5 Se arr the Gockighelt Gos'ef Ina vhs apc tat aa 266. tt 
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