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TRANSACTIONS OF THE SECTIONS. 19] 
On the Limits to the Velocity of Revolving Lighthouse Apparatus caused by 
the time required for the production of Luminous Impressions on the Eye. 
By Wit.1aM Sway, F.R.S.E. 
The object of this communication was to ascertain the greatest velocity that can 
be communicated to a revolving lighthouse apparatus, without impairing the bright- 
ness of its flashes. The author referred to a proposal, by the late Captain Basil 
Hall, to combine the superior brightness of a revolving, with the constancy of a 
fixed light, by causing the flashes to succeed each other so rapidly as to produce a 
continuous impression on the eye. The efficiency of this plan was tested by Mr. 
Alan Stevenson, who has described his experiments in his Account of the Skerryvore 
Lighthouse, p. 313. He found that as the velocity of rotation increased, the appa- 
rent brightness of the flashes diminished ; and he explained this result, by supposing 
that the light had not had time to produce its full effect on the eye. 
The correctness of this explanation is satisfactorily shown by the author’s recent 
researches on the gradual action of light on the eye, published in the Transactions 
of the Royal Society of Edinburgh for 1849 ; which also afford the means of calcu- 
lating the greatest velocity that can be communicated to a revolving light without 
diminishing its apparent brightness. 
His experiments prove that lights of every degree of apparent brightness require 
nearly one-tenth of a second to produce their full effect on the eye ; from which it fol- 
lows, that the velocity of a revolving light must be regulated so that the duration of 
its flashes may exceed one-tenth of a second. This velocity is easily calculated, by 
first ascertaining the minimum divergence of the rays from the expression ptt in 
a 
which « is the divergence of the rays, ἐ the duration of a single flash, and ¢ the time 
of a complete revolution. The author stated that for the great lens of Fresnel’s 
dioptric apparatus of the first order, the velocity of rotation could not be made to 
exceed one revolution in eight seconds, without necessarily impairing the brightness 
of the light. 
On a Gas Stove. By Witt1am Syxes Warp, Leeds. 
The novelty of this consists in constructing the stove in a vertical position so as to 
expose considerable surfaces for the absorption of heat from gas burners, and for 
the radiation of the heat ; and from that. flatness of construction the apparatus oc- 
cupies little space, not projecting into the room more than 2 or 3 inches, being thus 
productive of little inconvenience when out of use. 
A plate of thin sheet-iron is fitted into an ordinary fireplace in the manner of a 
fireboard, about 2 inches within the projection of the mantelpiece; about 3 inches 
in front of the back plate a similar plate of sheet-iron is secured by bolts; a third, 
somewhat smaller, plate of iron is about 1 inch from the second plate, and enclosed 
at the top, bottom and sides, so as to form a chamber of about 2 to 3 feet square 
and 1 inch in thickness. Towards the bottom of the last plate a long aperture is 
cut, closed by a sliding plate, acting as a door for lighting the gas jets and admitting 
a small quantity of air. A little below the aperture a pipe is introduced, in which are 
fixed three or more gas jets, either the ordinary small batwing burners or tips with 
two or three boles, so that the flames may extend laterally, not coming into imme- 
diate contact with the air. From the top of the enclosed chamber a pipe of 12 
inch in diameter proceeds through the second and first plates into the chimney of 
the apartment. 
The author found that his apparatus was sufficient to raise the temperature of a 
moderate-sized room from 5 to 10 degrees Fahr., with a consumption of about 3 feet 
of gas per hour, costing about twopence for ten hours, and that it was particularly 
useful in warming a bedroom where only a slight elevation of temperature was re- 
quired, and perfectly free from the production of dirt or the slightest smell. 
None of the products of combustion entered into the room, and the ventilation 
was improved rather than impeded. 
