114. W.S. Gilman, Jr., on the Aurora of April, 1869. 
brought out at a convenient point above the assistant’s desk. 
e former was provided with two cocks, one to regulate the 
flow of water and another for emptying it in cold weather. 
At 3 feet above a shelf of the desk, a branch was fitted to 
the air-pipe which was connected by rubber to a vertical glass 
tube whose lower end stands in a small vessel of mercury and 
serves as a manometer. This arrangement was put u 
lumber in two days’ time and gives the full Torricellian va- a 
cuum less the tension of water-vapor. 
For the working students, four similarly constructed pumps 
were made, each being in the center of a double table that ac- 
commodates four operators. In case of these pumps it was not 
practicable to place the pipes within flues ; so they are carried 
up to the ceiling of the laboratory, a height of 13 feet, and 
the fall-pipes pass below into a drain in the cellar bottom. 
The pipes are supported on the faces of a narrow vertical plank 
secured above to the ceiling, and below to the reagent shelf. 
The glass manometer-tube is brought into a slot in this plank 
so as to stand in full view of all four operators. The water 
supply is regulated from either side of the desk by a cock with 
a double lever-handle eight inches long, which works against @ 
stop when open to the. point of maximum exhaustion. The 
air-pipes terminate in a horizontal brass tube screwed on a shelf 
and open at either end for connecting with the filtering appa- 
ratus. These pumps when in action support a column of mer- 
cury of about 19 to 20 inches, which is sufficient for most ordi- 
nary purposes, and their use is in great favor with the students. 
It is needful to intervene between the filter flask and the metal 
pipes a small bottle to collect the liquids which condense in the 
latter, as they contain lead in solution or suspension. 
Art. XIII—On the Aurora seen in New York, April 1, 
1869; by W. 8S. Gruman,.Jr. (In a letter to Prof. Ex1as 
Loomis, Yale College.) 
I sewn herewith a brief account of the grand aurora of last, 
evening, as seen by a party of three from the roof of the Ob- 
servatory of Mr. Jacob Campbell, in Brooklyn. 
On coming out of doors to go to the Observatory at 4 past 
7 in the evening the writer called the attention of one of the 
streaky clouds pointing upward from the horizon, — 
inning of an auroral display. — 
aad remarked that it was the beg: g 
Hardly had we paused when by their changing, wavy light we 
perceived we were not in error, and ina few minutes afterward 
saw the formation of the corona as in the sketch below. 
ee es | 
7 
Sti gis aaa 
Pea | Rone ae 
