ON FOG SIGNALS. 109 
be charged with the general control, and in particular with making the sig- 
nals. These should be observed from various points, at Portsmouth and on 
the Isle of Wight, so disposed as to give a series of distances from two to ten 
miles, if possible—and so distributed that some may always have the signal 
up, others down the wind, which is an essential condition. 
* Portland seems also to be very suitable, or perhaps Weymouth. 
“‘Coast-guards or other local officials can probably be found at any of 
these stations to observe the signals; but, in any case, it is necessary that 
the persons engaged should be habitually on the spot, so as to profit by the 
occurrence of a fog without any delay. 
«The process would be of this sort :— 
** When the fog seems to the directing officer sufficiently thick, he sends 
word to the different observers of the time and nature of the intended sig- 
nals; he and they then measure the fog by the means already suggested, or 
some equivalent. 
«<The signals, if fully carried out, should be— 
“1. Guns. 
«2. Bells, gongs, drums. 
«3. Steam-whistle, blown by steam from a small boiler, and by air con- 
densed to the same pressure (unless it be found that both sounds are equally 
audible). The pressures should be recorded. 
“‘4, Two organ-pipes, one whose pitch can be varied at pleasure, the other 
with a reed, connected so that they can be blown together or separately. 
**5, Holmes’s trumpet, Daboll’s, or any other which appears to deserve a 
trial. 
«6, A Siren of 8 inches diameter, supplied with water by a hand-pump 
under a head of about 30 feet (which head must be recorded): by increasing 
the pressure, the pitch rises. 
“7, An organ-pipe of variable length, to be sounded under water as the 
Siren. 
*‘ The chief points to be attended to in these signals are— 
“1. The relative efficiency of guns of various calibre, and with varied 
charges of powder. 
* 2. Weights of bells, and force of blows, measured by the weight and fall 
of the hammers. 
«3. In the wind instruments, the effect of varying the pressure. It is 
probable that each will have some appropriate force of blast which will give 
a maximum result. 
«<4. The two pipes are first to be sounded separately on the same note, to 
ascertain if the reed have any advantages. Then the variable one is to be 
gradually sharpened through a considerable range, to find what pitch is best 
for distance; and lastly, both sounding in unison, one is to be sharpened, so 
as to examine the influence of concords and discords through a large portion 
of the scale. They should be sounded not only continuously, but also with 
short interruptions. 
“5. The Siren should be tried in a metallic cylinder, to learn if this will 
intercept its sound. If so, by making apertures in the cylinder and causing 
it to revolve, it may be as possible to identify such signals as revolving lights. 
“Each observer, when he hears these signals, should note the time and his 
impression as to their distinctness. He should also try how near he can 
estimate their direction. For this purpose (unless he can thoroughly depend 
on his freedom from bias) he should be blindfolded and turned about to lose 
his bearings. He should also try, as above suggested, the aid of acoustic 
