45^5 



NA TURE 



[Oct. I, 187, 



and for small distances becomes inap|ireciable. In connection 

 with this I may mention tliat bromide plates, even when backed 

 with a non-actinic backing in optical contact with the plate, will 

 give irradiation with alkaline development, whilst with acid 

 development the irradiation will disappear. The explanation 

 is not far to seek — the alkaline development reduces the silver in 

 situ, the acid development deposits silver on the surface and where 

 there is most attractive force. In the former case, the dispersed 

 light acting on the interior of the film, causes the necessary 

 change in the bromide of silver to effect reduction. Daguer- 

 reotype plates are not free from irradiation as has been supposed, 

 though, owing to the extraordinary thinness of the iodide of 

 silver, but little effect can be traced unless very prolonged 

 exposure be given. 



In the dry process selected for the transit of Venus it has then 

 been thought desirable to have a rather dense film containing 

 a proportion of iodide of silver and a colloid body — alburnen — 

 as preservative. I am not unmindful of the fact that different 

 pyroxylines more or less affect irradiation, and we have altered the 

 constitution of the pyroxyline inj the collodion I shall use, by 

 adding certain proportions of water ; this materially aids the an- 

 nihilation of irradiation from these plates. 



For registering the time of external and internal contact of the 

 planet with the sun's <lisc, the method known as Janssen's has 

 been adopted, viz., causing a fresh portion of a plate to be exposed 

 every second during the critical time, to the sun's limb, at that 

 part where the contact will take place. Mr. Christie and -Mr. 

 De la Rue have both devised a slide for this purpose. The 

 English parties use that designed by the former, M'hilst Colonel 

 Tennant will use that by the latter. Shrinkage in the film has 

 been carefully looked for by Dr. Vcgel, oi Berlin, and also by 

 myself. Photographing a grating of 200 lines to the inch by 

 contact printing, and measuring the results, I have been unable 

 to find any alteration in the distances of the lines at any part of 

 the film, hence I feel confident that any shrinking that can take 

 place will be so small as to be negligible. The Russian parties 

 are, I believe, going to use a grating material of iron wires. If 

 shrinkage does occur this would be necessary, but it seems almost 

 useless, in fact hurtful, where there will lie none. There must 

 be a certain error introduced due to the grating itself. The 

 method of finding the angle of the position of the wires will be 

 determined photographically. Two pictures of the sun will be 

 taken at an interval of one minute on the same plate. The line 

 forming the intersection of the sun's images will give the angle of 

 position of the wires when measured by the micrometer. At 

 each station the photographic party will consist of one officer 

 and three sappers, all of whom have been trained in the use of 

 the photo-heliograph and the process employed. A drill for each 

 operation has been devised, and it is anticipated that the dangers 

 of excitement during the critical times have been overcome by 

 this arrangement. Practice on a mock transit has ensured a 

 thorough knowledge of each phase of the phenomena ; and I 

 appi'ehend that discipline combined with a trust in their superiors 

 will have annihilated one source of failure. 



On the im/'ortancc 0/ iinprofcd inetliods of Jicgistralion of Wind 

 on the Coast, with a tioti<:e of an Anemometer, designed by Mi: 

 W. De la Riu, F.R.S., to furnish telegraphic information of the 

 occurrence of strong winds, by Robert H. Scott, M.A., F.R.S. 



It is hardly necessary to draw the attention of the Section to 

 the fact that the configuration of the earth's surface exercises an 

 overwhelming influence on the wind both as to its direction and 

 force. Some statements and tables contained in a paper of mine in 

 the last number of the Quarterly Journal of the Meteorological 

 Society * abundantly prove this assertion, and it is therefore easy 

 to see what an imperfect representation of the actual force of the 

 wind at sea can be furnished by reports from a broken and moun- 

 tainous coast, such as the Atlantic coasts of Ireland and Scotland, 

 where the telegraiihic stations are perforce situated in sheltered 

 places, inasmuch as j-.arbours are naturally found \\here there is 

 as little exposure to wind as is possible. 



In the praclicc of weather telegraphy and storm warnings, as 

 tie number of reports received per day from each station is 

 s'rictly limited, on financial considerations, it is quite obvious 

 tliat if the acluil epoch of the commencement of a gale does not 

 fall within the hours of attendance at the Telegraphic Office and 

 at the Mcteoiological Office, which practically only extend from 

 8 A.M. till 3 r.M., much time will be lost in sending news of the 

 » " An altempl lo establish .-i Relation between the Velocity of the Wind 

 and its Force (lieaufort Scale), with some remarks on Ancmomelrlcal observa- 

 tions in General," by Robert ,.Scott, I'.R.S. Quart. Jouni. of Met. .Soc. 



fact to London. If it commences at 6 r.M. at Valencia, we 

 cannot hear of it in London till 9 a.m. next morning. 



On the other hand, if the observer be living in a sheltered spot, 

 such as Plymouth, Nairn, or Greencastle, we shall not get a true 

 report of the gale at all, inasmuch as the observer will not have 

 felt it himself. 



The fir^t-named defect in our system can only be met by a 

 considerably increased expenditure on the service, and that is 

 not a scientific, but an administrative question, with which the 

 Government can alone deal. 



In order to meet the second difficulty, Mr. De la Rue has 

 kindly devised an instrumental arrangement, by which the fact of 

 any given force of wind having been reached at an exposed point 

 (such as Rame Head for Plymouth, or Malin Head for Green- 

 castle), can be at once conveyed to the reporter in his own office, 

 or even to the central office in I>ondon. The instrument has 

 been made by Messrs. Negretti and Zambra. 



The following is the construction of the new signalling anemo- 

 meter. 



To the ordinary Robinson's anemometer spindle is affixed a 

 toothed wheel, which is geared with another and larger toothed 

 wheel fixed on a second vertical spindle which carries a centrifugal 

 governor. The governor spindle is made to rotate at one- half 

 or one-third of the velocity of the anemometer spindle in order 

 that the rods carrying the governor balls may not have to be 

 made inconveniently short. A provision is made for adjusting 

 the length of the arms of the governors so that different wind 

 velocities may be indicated within certain limits. 



The governor balls act in the well-known way and expand 

 when driven at a given rate, and the upward motion of these 

 governor balls is used to raise a secondary wheel to bring into 

 gear a third spindle on which is fixed the armature of a magneto- 

 electric apparatus, which, like Sir Charles Wheatstone's instru- 

 ments, consists of a compound permanent magnet with four soft 

 iron cores, two of which are mounted on the north pole of the 

 nngnet and two on the south pole ; these iron cores are surrounded 

 witli fine insulated copper wire, and on rotation of tire armature 

 give alternate + and — currents, in rapid succession according to 

 tlie rate at which the armature is driven. These currents are con- 

 veyed inland to the observing station by insulated wires, and give 

 warning l^y ringing an alarum as long as the anemometer cups 

 are revolving at a velocity sufficient to raise the governor balls so 

 as to bring tlie magneto-electrical apparatus into geir. 



We see, therefore, that by adjusting the governors of the ap- 

 paratus to indicate any required speed, a warning will at once 

 be given when the wind reaches that speed, be it that of 60, 40, 

 or 20 miles an hour, as may be required. 



All the attention which the instrument requires after the 

 apparatus is fixed is to lead two insulated wires Irom the anemo- 

 meter into the observing station, and to connect these wires to 

 the two terminals on the alarum. 



In order to enable the observer to communicate at once and at 

 as little expense as pos?ible, to London, the fact of the velocity 

 in question having been reached, the individual stations might be 

 known by letters or symbols which might simply be telegraphed 

 to Londoa as an announcement that the alarum was acting at the 

 station in question. 



It is obvious that this plan is exceedingly simple, and there 

 seems little reason why it should not be thoroughly eflicacious, if 

 only the [registering portion of the apparatus can be properly ' 

 protected from wilful damage by mischievous persons. 



As usual, we are met by the question of cost, not only of the 

 apparatus but of the connecting wires, and last, though not le.ast, 

 of the transmission of the messages. To enable us to render our ' 

 service more effective than it is we must be supplied with the 

 sinews of war. The 3,000/. which is the very utmost we spend | 

 annually on telegr.aphy, including s.i!aries, rent, and every item, 

 is but small compared wfth the 50,000/. entirely exelusi^'e oj 

 salaries with which the chief signal office of the United States is 

 so munificently endowed. } 



On the Source from which the Kinetic Energy is drawn which 

 parses into Heat in the Afoz'cment of the Tides, by John Purser, 

 M. R.I. A., Professor of Mathematics in the (Jiiecn's University. 



Attention has of late years been directeil by .Mayer, Prof. Janus 

 Thomson, and others, to the fact that the friction of the tiilal 

 currents on the bed of the ocean exercises an effect in retarding 

 the eartli's rotation on its axis. 



The late eminent French astronomer, Delaunay, was the fir-i, 

 as far as I am aware, to form a numerical estimate of the posoiMe 

 magnitude of this effect, and to suggest that it furnishes a not 



