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with about the same force ; but, strange to say, the luminous rays repelled the black surface with more energy than the white one. Mr. Crookes has also constructed an instrument which he calls a "radiometer," and which excited much attention and interest, both at the soirée of the Royal Society and the meeting last week. The apparatus consists of four arms, suspended on a steel point resting on a cap, so that the arms are able to revolve horizontally upon their central pivot, just the same, in fact, as the arms of an anemometer revolve. To the extremity of each arm of straw in the apparatus made by Mr. Crookes, is fastened a thin disc of pith, white on one side and black on the other, the black surfaces of all the discs facing the same way; the pith discs are each about the size of a sixpence. The whole arrangement is enclosed in a glass globe, which is then exhausted to the highest attainable point and hermetically sealed.
This arrangement rotates with more or less velocity under the action of light. With one of the instruments, the arm revolved once in 182 seconds, when a candle flame was placed at a distance of 20in. When the same candle was placed at a distance of 10in., one revolution in 45 seconds was the result; and at 5in., one revolution was given in 11 seconds. Thus, it will be seen, that the mechanical effect varies almost exactly inversely with the square of the distance, so that theory and experiment coincide.
In these experiments, Mr. Crookes had to be very careful to guard against the effects of undesired radiation. The lighted sun burners in the roof of the hall of the Royal Society, interfered with some of the results, and a candle placed incautiously near his bulbs, would send the contents of some of them spinning. As the velocity with which they spin varies with the intensity of the light, in these instruments we have a new form of actinometer. The action of the radiometer has not yet been explained.
VOLUME XLIV.No. X.
THE OWNER'S LOAD-LINE.
N our number for May last we reviewed, at some length, the
whole question of load-line legislation and advocated the incorporation of an "owner's load-line " with the Government
Bill. Everyone knows the history of that Bill, and also of the short and temporary Act which has, since then, been put in its place, As is indicated by the title of this article, we are not now going into the whole question of the recent legislation, but we congratulate our readers and all who have at heart the true interests of the Mercantile Marine, on the highly satisfactory circumstance that although the new Act was passed under great excitement, it is not itself a piece of sensational legislation. It is merely a development of the old policy of the Board of Trade, an application of the principle that it is not the province of Government either to direct or to certify, but it devolves upon Government to inspect, and where necessary to correct or to condemn ; they should interfere to prevent or to punish wrong doing, but they should take no portion of the responsibility away from the shipowner whose business it is to make and to keep his ship seaworthy. The “ owner's load-line” clanse is in no wise a concession to the advocates of the paternal policy, who wish Government to prescribe for the shipowner how his ship shall
The proposal that the owners of ships should themselves be compelled to fix the limit of immersion of their ships, originated with the officers of the Board of Trade. Although there is no doubt that this question was fully discussed within the mystic circle, we believe it was first
formally brought before the public on the occasion of a discussion on the freeboard question at the Institution of Naval Architects in 1872, by Mr. J. McFarlane Gray. The plan was again brought forward by him at the meeting of the Institution in 1874. His plan, however, also contained a provision for increasing the tonnage upon which dues are paid or diminishing it, according as the marked load-line is above or below the immersion contemplated when the Tonnage Act was framed.
Our readers will remember that in the early part of the present session Mr. Norwood brought in a Bill, entitled the “ Merchant Shipping (LoadLine) Bill,” of which the proposal for an owner's load-line was the chief feature. The clause in the new Government measure which has passed into law is substantially the same as that of Mr. Norwood. The load-line is to be marked by a ball of sufficient size to be visible, having a horizontal line drawn through its centre, the line indicating the intended load-line in salt water. It is also provided in addition to Mr. Norwood's clause, that lines shall be marked outside every ship, showing the position of her decks, that any one may see how much freeboard she has from the various decks. We think the Board of Trade advisers have raised a very serious question in requiring the marking of the decks to the upper sides amidships, because if an owner puts thick balks of timber there, he will get an advantage over another who has a stronger but thin iron deck.
It is made clear by the Act that the Board of Trade do not certify the load-line in any case ; a record of it is to be delivered by the owner to the Customs, but it is not to be officially recorded by the Board of Trade. Any action by the Board of Trade, whereby they should be a party in any way to fixing a load-line, would be to ignore the intention of the Legislature. Government does not intend to prescribe the load-line; the mark is to be declaratory of the owner's intention, and of the intention of no one else. It is to give the same information which would be conveyed by the ship's immersion when completely loaded. Its effect will be that a ship can be dealt with legally as regards overloading from the period when its mark is put on, instead of, as heretofore, at the last minute, just as it is about to put to sea. It was said that when no ship could be stopped without communicating with Whitehall, so much time was often lost, that an overladen ship escaped while telegrams were passing about her. This state of things will be altered by the new arrangement, and in addition the marked load-line virtually indefinitely extends the time between loading and sailing, and the effect must be to make assurance doubly sure. Another effect it may have, perhaps not altogether so beneficial as has been supposed. It is said, and with much truth, that shipowners will not mark their vessels for so deep a line as they would venture to load