10 
SHORT NOTES ON PROFESSIONAL SUBJECTS. 
case accelerating, beginning with 0° and terminating with 6° (1 turn in 30 calibres) 
at tbe muzzle. There are two projectiles,—common shells, with percussion fuzes, 
and solid steel shot: of the latter there are two varieties, flat-fronted for close 
quarters, pointed for more distant fire. 
The annexed sketch of the breech screw, vis de culasse, and tin cup, obturateur, of 
the 9*4 inch gun will sufficiently explain the system of breech closing. The end of 
Screw for closing the breech of the French rifled canon de *24 (9‘45 inch) 
with the tin cup. 
the bore is tapped with a coarse female screw and closed with a solid screw plug; to 
facilitate the admission of the plug, the male and female threads are removed on 
three lines, over a width equivalent in each place to one-sixth of the circumference. 
Thus one-half of the thread is removed, and the projecting portion of the male thread 
passes along the space left by the cutting away of the female thread, until the plug 
is home, when a turn of 60° engages all the remaining threads and makes fast the 
breech. No advantage is claimed in respect to rapidity of fire. La vitesse du tir 
serait an moins d’un coup en dix minutes , a statement so modest, that we quote the 
words. 
The guns are used on iron carriages and slides of the box girder construction, 
and very low. Those of the 9*4 inch gun weigh 6 tons 8 cwt. 6500 kilo, but can 
it is said be worked by 20 men at sea and by 14 in harbour. The system of com¬ 
pression seems to resemble our vice compressor, the friction being taken on the 
sides of the slide. 
16. Kule for finding heights by the aneroid.* Multiply 26,300 by 
the difference between the readings of the aneroid, and divide the product by half 
the sum of the readings; the quotient will be the height uncorrected for temperature. 
To find the correction depending on the temperature:—Multiply the difference 
between 32 and half the sum of the temperatures at the lower and upper stations 
by 2 3 and by the number of thousands of feet in the uncorrected height. The 
product will be the correction, which must be added to or subtracted from the 
uncorrected height, according as half the sum of the temperatures is greater or less 
than 32. 
* Sufficiently accurate for any height, of less than 10,000 ft.—By G. Harvey Simmonds, Esq. 
[Extracted from the Proceedings of the Meteorological Society]. 
