OBSERVATORIES AND INSTRUMENTS. 



681 



the arrangement of the normal clock. To cor- 

 rect that which, in the present perfection of 

 workmanship, is the principal one of three 

 sources of error namely, that the mercury, 

 owing to the greater ratio of its mass to its 

 amount of surface than holds true in case of the 

 rods, is slower than the latter in responding to 

 changes of temperature, thus preventing exact 

 compensation and the uniformity desired in the 

 effective length of the pendulum the clock is 

 now placed in a subterranean chamber beneath 

 the hall, where changes of temperature occur 

 very slowly, and their limits from one period 

 of the year to another are very narrow. It is 

 intended, further, to remove a second cause of 

 error the barometric, or that due to unequal 

 resistances of the air at different densities to 

 the movement of the pendulum by enclosing 

 the clock within an air-tight case, and, by 

 means of a pressure-gauge and an air-pump 

 communicating with the enclosed space, main- 

 taining about the clock an atmosphere of uni- 

 form density. Dr. Winnecke, of the same ob- 

 servatory, is directing his attention to the de- 

 termination of the parallax of fixed stars, re- 

 cording his results by the automatic method. 



Other European Countries. In respect to 

 these, little information has been obtained. In 

 Italy, astronomical observations are still carried 

 on with the zeal and the success also for which, 

 in this respect, that country has so long been 

 honorably distinguished ; and, in particular, it 

 may be remarked that Father Secchi, at Rome, 

 and M. Donati, at Florence, are actively prose- 

 secuting the work of celestial exploration and 

 discovery. A meteorological bulletin, similar to 

 those of Paris and St. Petersburg, is now issued 

 from the Royal Observatory at Palermo. A 

 Central Meteorological Bureau was, May 1, 

 1865, instituted in Russia. As in France and 

 Russia, reports of meteorological phenomena 

 from various stations will be regularly received 

 by the bureau, and bulletins issued by it, con- 

 taining especially whatever relates to the prog- 

 ress of storms, will be placarded in the princi- 

 pal seaports. 



Time- Signals. Three principal methods of 

 transmitting to distant points, and there re- 

 peating or signalling, the correct time of a 

 standard or normal clock, have been resorted 

 to. These are, 1, that of the electric-fixed time- 

 gun; 2, that of the electric-dropped time-ball; 

 and 3, that of electric-controlled clocks. All 

 three of these methods have been adopted in 

 the transmission of correct time from the clock 

 of the Royal Observatory, Edinburgh ; though 

 the controlled clock and the time-gun have 

 been most in demand. In the former case, here 

 and in other parts of Great Britain, the ar- 

 rangement known as Jones' patent has been 

 employed; and on this plan several clocks in 

 different parts of Edinburgh have been made to 

 keep [sensibly] exact time with that of the Ob- 

 servatory. The time-gun, 4,000 feet from the 

 Observatory, required a permanent use of the 

 transmitting wires, so that the mode was 



scarcely applicable to great distances. Mr. N. J. 

 Holmes then arranged a time-gun at Newcastle, 

 120 miles distant, to be fired by means of 

 Wheatstone's magneto-exploder and Abel's 

 magnetic fuse; and on a fair day the current 

 sent off along the telegraph wire discharged 

 the gun with no sensible hesitation or "hang 

 fire ; " but on a foggy day the highly intense 

 magnetic current was in too great a degree 

 dissipated and lost. A practical system was 

 finally devised, by causing a large signal-send- 

 ing clock to discharge along the line of tele- 

 graph wire, at the due moment, a galvanic cur- 

 rent of low intensity ; this, on reaching New- 

 castle, was made to liberate in the proper ap- 

 paratus there the more intense magnetic cur- 

 rent, which had then only a few hundred yards 

 to travel to the gun. Several time-guns at dif- 

 ferent places have since been put in operation, 

 the Government favoring these enterprises by 

 lending 24-pounders for use in them. At some 

 points the plan, once tried, had been abandoned ; 

 but there were still (in the beginning of 1864) 

 fresh applications from others for the benefits 

 of the system. 



An important extension of time-arrange- 

 ments from the Greenwich Observatory and 

 from other points has been up to at least the 

 spring of 1865 going forward in England. 

 Mr. De la Rue has made an electric communi- 

 cation of his establishment with Greenwich 

 the clock of the former being caused for months 

 consecutively to beat second by second with 

 the Observatory clock at the latter ; while, to 

 correct an occasional variation, should such 

 occur, a special signal is also sent at four sec- 

 onds after every hour. Mr. C. F. Varley has 

 mounted apparatus for distributing time-sig- 

 nals over various lines of railway reaching al- 

 most to the extremities of Britain, and for 

 firing signal guns at Newcastle and Shields. 

 The currents sent hourly to the office of the 

 London District Telegraph are made available 

 to chronometer-makers of the city. Prof. Airy 

 expresses the hope that movements will soon 

 be set on foot in London for the more perfect 

 regulation of public clocks- generally, and for 

 other exhibitions of time-signals. Liverpool is 

 to have a time-gun controlled from her Observ- 

 atory; and at Glasgow, ten public clocks at 

 distances averaging three miles are in opera- 

 tion, controlled from the Observatory there. 



Mr. De la Rue describes an ingenious method 

 of communicating the time-signals or impulses 

 from the normal clock at Pulkowa for control- 

 ling the time of other clocks, On the frame of 

 the clock, one on each side of an imaginary 

 plane that would cut the centre of the crutch, 

 are fixed two ivory cylinders, each having 

 cemented within it a capillary tube of glass : 

 through these tubes, from reservoirs of that 

 liquid metal, flow streams of mercury, which 

 meet and coalesce in one, thus constituting a 

 mercury wire that, so long as it is continuous, 

 serves to complete the circuit of a battery. la 

 order to break the circuit at the desired inter- 



