Dr. Hare’s improved Eudiometers. 21 
sembled the results of all existing observations on the height, 
velocity, and movement of fire-balls in the 2d, 3rd, and 4th 
division of my work, which ought to be known previously to 
a person’s forming an opinion on the origin of meteors. Be- 
sides, having mentioned with every phenomenon the sources 
whence I took my account, the further details may be easily 
found by referring to them; and finally, I have in the last di- 
vision of the work drawn together the results of them, by 
which the proofs of their cosmical origin, and of the impossi- 
bility of their being the produce of our earth or our atmo- 
sphere, are elucidated in the simplest and most natural man- 
ner. 
II. An Account of some Eudiometers of an improved Construc- 
tion. By Boxsert Hare, M.D. Professor of Chemistry in 
the University of Pennsylvania. 
N the second volume of the American Journal of Science 
I published an account of some eudiometers, operating by 
a mechanism which, previously, had not been employed in 
eudiometry. A graduated rod, sliding into a tube through a 
collar of leathers soaked in lard, and compressed by a screw 
so as to be perfectly air-tight, was employed to vary the capa- 
city of the tube, and at the same time to be a measure of the 
quantity of air, or of any other gas, consequently drawn in or 
expelled. About one-third of the tube was occupied by the 
sliding rod. The reniainder, being recurved and converging 
to a perforated apex, was of a form convenient for with- 
drawing measured portions of gas from vessels inverted over 
water or mercury. 
There were two forms of the sliding rod eudiometer: one 
designed to be used with nitric oxide, or with liquids absorb- 
ing oxygen; the other, with explosive mixtures. The latter 
differed from the eudiometerss for explosive mixtures previously 
invented, in the contrivance for exploding the gases, as well as 
in the mode for measuring them; a wire ignited by galvanism 
being substituted for the electric spark, as the means of in- 
flammation. 
I shall proceed to describe several eudiometers, operating 
upon the principle of those above alluded to, with some mo- 
difications suggested by experience. Fig. 1 represents a 
hydro-oxygen eudiometer, in which the measurements are 
made by a sliding rod, and the explosions are effected by the 
alvanic ignition of a platina wire, as in an instrument formerly 
escribed: excepting that the method then employed of ce- 
menting the platina wire, in holes made through = ee 
laving 
