52 



NATURE 



{May 1 8, 1876 



amount of correction required, the two chronometers are 

 compared, usually by watching for a coincidence of beats. 

 Knowing the error of the sidereal standard, by astro- 

 nomical observation as described, the true sidereal time 

 of comparison becomes known ; the corresponding mean 

 solar lime is then easily calculated, and the error of the 

 mean solar system of clocks immediately found. The 

 commutator handle is then turned to throw a battery 

 current into the accelerating and retarding coil, such as 

 will attract or repel the pendulum magnet of the Mean 

 Solar Standard, according as the clock is found to be 

 slow or fast. The Mean Solar Standard and the various 

 clocks in sympathy with it (those driven by it at Green- 

 wich and those controlled by it at London) all receive the 

 same correction, and are all brought to exact Greenwich 

 mean time. By the arrangement described it will be seen 

 that the Superintendent of the Time Department can at 

 any time refer the Mean Solar system of clocks to the 

 Sidereal Standard, and find and correct the error of the 

 Mean Solar Standard and the whole system of mean 

 solar clocks, whilst engaged in his ordinary office duties, 

 and without moving from his position in the Computing 

 Room. Correction is usually made every morning before 

 I oh. A.M. (because at that hour an important distribution 

 of time takes place), and again before ih. P.M. (another 

 important hour as regards time signals). The correction 

 required is usually only a small fraction of a second. 



Having shown how the error of the Sidereal Standard 

 at Greenwich is found by astronomical observation, 

 and from it that of the Mean Solar Standard, and 

 lastly, how the latter clock is adjusted to exact time, 

 we now proceed to describe the arrangements for giving 

 time signals to the external world. A galvanic circuit 

 passes through the Mean Solar Standard, but is broken 

 in the clock in tv;o places ; one of these is united from 

 about half a minute before to about half a minute 

 after the minute hand marks sixty, and the other when 

 the seconds hand indicates sixty seconds precisely. Both 

 breaks can therefore only be together united at the com- 

 mencement of each hour, and then only can a current 

 pass. Each hourly current acts upon two electro-mag- 

 nets. One of these automatically discharges the Green- 

 Avich time-ball at ih. daily ; the other is the electro-mag- 

 net of the hourly signal relay (shown to the left in the 

 drawing) which completes various independent circuits, 

 each in connection with a separate line of wire. One of 

 these is in communication with the central telegraph 

 station of the General Post Office, London ; another 

 extends to the London Bridge Station of the South- 

 Easttrn Railway Company. Along each line a galvanic 

 signal passes hourly from the Observatory, day and night, 

 for further transmission by apparatus under the control 

 of other parties, and at this point (excepting in the case 

 of the Deal time-ball to be hereafter spoken of) the special 

 responsibility of the Observatory terminates. The small 

 bell and galvanometer in the drawing marked respec- 

 tively "Post Office Telegraphs" and "S.E.R. Hourly 

 Signals," indicate at the Observatory the passage of the 

 signals on these wires. 



( To be continued.) * 



THE OPENING OF THE LOAN COLLECTION 



'T*HE Loan Collection was auspiciously opened on 

 -*- Satui-day last by the visit of the Queen, and that 

 it has exceeded all expectations is sufficiently shown 

 by the opinions of the public press, which we have 

 collected in another page. The Queen's visit is 

 admitted on all hands to have been a complete suc- 

 cess. Her Majesty herself, the Empress of Germany, 

 and the other distinguished personages who accom- 

 panied her, showed a genuine interest in the collec- 

 tion, and especially in those apparatus to which their 



attention was particularly drawn. The Times is " autho- 

 rised to say that not only did her Majesty express to the 

 Lord President of the Council, the Duke of Richmond, 

 her gratification with the exhibition and with its success 

 — exceeding any that could possibly have been antici- 

 pated of it — but that her Majesty desired to make known 

 how much she was gratified by the manner of her recep- 

 tion and by the solicitude with which her visit was made 

 interesting by the several scientific men who explained to 

 her the nature of the objects exhibited." 



Besides the German Empress, the Queen was accom- 

 panied by the Princess Beatrice, the Duke of Edinburgh, 

 the Duke of Cambridge, Prince Edward of Saxe-Weimar, 

 and among others who accompanied the Royal party 

 during their tour round the collection were the Duke of 

 Sutherland, the German, Austrian, Russian, and French 

 and Spanish Ambassadors, the Italian Minister, the 

 United States Charge d'Affaires, besides'a considerable 

 number of the most eminent representatives of British 

 and Foreign science, most of the members of the several 

 committees, and many of the exhibitors. 



The Queen was received at the south-eastern entrance 

 to the Exhibition by the Duke of Richmond and Gordon 

 and the Vice-President of the Committee of Council on 

 Education, Lord Sandon, M.P., by the Commissioners of 

 the Exhibition of 185 1, upon whose premises the Exhibi- 

 tion is held, and by the members of the Duke of Devon- 

 shire's Committee on Scientific Instruction. 



The Duke of Richmond and Gordon escorted the Queen 

 round the Exhibition, pointing out objects of interest, and 

 as the Queen entered each division of the galleries, gentle- 

 men conversant with the various branches of science had 

 the honour of being presented and of explaining to their 

 Majesties and Highnesses the objects exhibited. 



The Educational Collection was first examined, M. 

 Heard showing the curious and extensive Russian peda- 

 gogical collection. In the Mechanical Section the famous 

 primitive locomotives " Puffing Billy " and the " Rocket " 

 attracted considerable attention. In this section also 

 the ship Faraday was described by Dr. C. W. Siemens, 

 who at the same time explained his bathometer, recently 

 described in Nature. The German ironclad, Konig 

 Wilhelm, and other beautiful models illustrating the 

 applications of science to shipbuilding, including a model 

 of the Serapis, were described by Mr. E. J. Reed and the 

 Duke of Edinburgh. In this same section Mr. W. Froude 

 showed his models of the hulls of ships in solid paraffin, 

 by which the valuable experiments were made which were 

 recently described by him at length in Nature. Prof. 

 Tyndall's explanation of the lighthouses and fog-horns 

 excited considerable interest, the Siren fog-horn being 

 sounded to illustrate the usefulness of the signal. In the 

 Fish Museum Mr. Frank Buckland was ready to explain 

 the many interesting objects and processes shown there. As 

 the party passed into the gallery of Electricity and Mag- 

 netism, the enharmonic organ of Perronet Thomson was 

 heard fiom above playing " God save the Queen." In the 

 section just mentioned M. Breguet, of Paris, gave a 

 brilliant display of the electric light, while Prof. Carey 

 Foster explained the great Haarlem natural magnet. 

 Mr. Gramme's magneto-electric machines were shown 

 Spottiswoode, and various telegraphic instruments by 

 by Mr. Culley. As her Majesty proceeded leisurely 

 through the collection, Sir William Thomson showed 

 his wonderfully ingenious tide - calculating machine, 

 Joule's apparatus for researches in heat, and an appa- 

 ratus for deep-sea soundings. Prof. Kennedy exhibited 

 the important collection of kinematic models sent by 

 Prof. Reuleaux, of the Royal Technical Academy, Berlin. 

 The Walter type-composing machine was explained by 

 Mr. J. C. Macdonald, Sir Joseph Whitworth described 

 his millionth-of-an-inch measuring apparatus, while Mr. 

 Chisholm explained various standard measures, a fine 

 collection of standards made for the Russian Govern- 



