212 REPORT—1858. 
and glistering star, and its power was sufficient to arrest the notice of the most care- 
less person at ten miles’ distance. No sky line was necessary to the distinctness of 
this remarkable signal, as is the case with semaphores and flags; indeed it was 
visible to the greatest advantage in front of a dark or hazy background. It could 
be used with equal facility from any spot where the sun’s rays reached it, as from 
between the trees of a forest or from a boat, as well as from a mast-head or a hill-top. 
It had another peculiarity, in being enabled to flash its messages in perfect secrecy, 
except to those who happened to be stationed in the narrow path along which they 
were sent. Many occasions would arise, especially in war time, where this invention 
would be of use. If the signaller was ignorant of the whereabouts of his correspond- 
ent, he must sweep the horizon with his flash until it had been seen, and a response 
elicited. For a more detailed description of this instrument, see the Proceedings of 
Section A. 
On the Economy of Water-Power. By Josrru Giynvn, F.R.S. 
In this part of England, and in other manufacturing districts where coal is found, the 
steam engine will generally be preferred to all other kinds of motive power ; but in 
many parts of the British empire, more especially in Scotland and Ireland, coal is 
scarce and water is abundant, and is now too often allowed to run to waste where 
its application to turn mills and to work machinery for farming purposes might save 
both time and money. 
Those machines produced at the Paris Exhibition, to which the writer would more 
particularly allude, are the horizontal water-wheels, some of which were wrongly 
named Turbines, whereas they were really substitutes for the machines so called. 
The Turbine is a machine of re-action, from which the water issues in jets, and 
the unbalanced pressure opposite the orifice impels the machine and causes it to re- 
volve in the opposite direction. It requires considerable skill in its construction, 
and careful attention when in use; but the horizontal water-wheel is a much more 
simple machine, and much less liable to derangement. The water drives round a 
fan with curved vanes, having a vertical axis and revolving in an iron case, the water 
escaping at the centre. 
The horizontal water-wheels in the French Exhibition consisted of two parts, or 
wheels, placed horizontally on a vertical axis, one wheel immediately above the other. 
The upper part or wheel is fixed, and serves to direct the water into the buckets of 
the lower one,—that is to say, the real water-wheel,—which revolves, and the axle 
or spindle revolves with it. 
The regulators, which determine the quantity of water and the speed of the wheel, 
may vary in almost every instance, some being mere wooden sluices, some being metal 
plates pierced with apertures like a ventilator, and some of stout leather strengthened : 
with iron plates, fitting on conical rollers and radiating from the axis. Some of these 
wheels are very powerful, and carry a spur-wheel upon the vertical axis, surrounded 
by six pairs of millstones for grinding corn, driven by pinions in the usual way ; 
other wheels, of smaller size and greater speed, drive a single pair of millstones, with- 
out the intervention of other mechanism, the axis of the water wheel being also the 
spindle of the mill-stone. 
The mechanical effect of these machines, when carefully made, is said to equal 
that of an over-shot or breast wheel. Some realize 75 per cent. 
On the Cause of Steam-boiler Explosions, and Means of Prevention. 
By J. Hopkinson. 
The author in this paper shows the necessity of increased attention to the form and 
construction of steam boilers. After noticing the hay-stack, waggon, Cornish, and 
Butterly boilers, he very fully describes the want of safety in the double fire-box boiler, 
and states the various causes of boiler explosions. He then says: ‘‘ I now propose to 
show you the patent compound safety-valve, which is a prevention against explosions 
from the causes before enumerated, and the explosions which have taken place from 
all causes excepting that of a defective boiler, as under all other circumstances steam 
boiler explosions are rendered impossible.” 
The patent compound safety-valve comprises two distinct valves, a large 5} inch 
diameter valve with flat face anda spherical or ball-faced valve 3 inches in diameter ; 
