25G 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[August, 



October 1843, when it was also suggested that the true time, at the different 

 towns, might also be shown for astronomical purposes. The dial of the 

 clock upon Granton Pier, Edinburgh, made by Mr. Bryson and which had 

 been finished for some time, was, by Mr. Walker's orders, made upon this 

 principle ; but for all ordinary purposes one minute hand, showing Green- 

 wich mean time, would be sufficient and no more inconvenience would be 

 experienced, than was now felt by the difference between mean and solar 

 time, by which clocks are a quarter of an hour before the sun at one season 

 of the year, and as much after the sun at another season. He thought that 

 engineers, particularly those who had the management of railways, would 

 confer a public benefit by advising and promoting an uniformity of time, 

 until that measure should be an effectual mode of accomplishing that desira- 

 ble object. 



Materials for pendulums. 



Mr. HoRNE said, that with regard to the material of the pendulums of 

 clocks, he had tried almost all the hard woods, and also gliss ; but he had 

 obtained the best result from using straight-grained white deal, well baked, 

 then painted and varnished, and lastly covered with gold leaf, with a coat of 

 copal varnish over all. This preparation had the additional advantage of 

 preventing the effects of damp. 



Mr. Giles stated, on the opinion of the late Mr. Troughton, that straight- 

 grained white deal, when well dried, was less subject to variation than any 

 other wood. When Mr. Giles was instructed by ihe late Mr. Rennie to take 

 the preparatory measurements for setting out the foundations of Waterloo 

 Bridge, as he could not take them directly across the river, he constructed a 

 platform of a quarter of a mile in length along the shore, and upon that 

 platform he laid down a line with extreme accuracy, by using three deal rods, 

 whicn he found retained their dimensions better than any other measuring 

 instruments. 



Mr. VuLLiAMY said, that he had recommended teak for pendulums, be- 

 cause it really was an excellent wood, and it was frequently more easy to be 

 procured of a proper quality, than to find deal which could be depended 

 upon ; but he principally approved of teak, because it resisted the attacks of 

 of the white ants in India and as it was not possible to foresee where clocks 

 might be sent to, it was better to provide for the possibility of their going to 

 the East, where a deal pendulum would probably not last above a few days. 

 He frequently used deal for pendulums of clocks that he knew would not 

 leave England, and he thought it, if properly prepared, a sufficiently good 

 material for pendulums. 



Mr. Davisom stated, in reply to some remarks on the difficulty of per- 

 fectly drying timber even when cut into small dimensions, that in his process 

 for seasoning casks the wood was frequently subjected to a current of air 

 heated up to 600° Fah. He was of opinion that if wood for pendulums was 

 seasoned by a similar process, and while hot was plunged into oil, the result 

 would prove very successful. 



Errors from variation in length and elasticity of the pendulum spring, 



Mr. Dent stated, that he had constructed, for Mr. Airy, the escapement 

 which had been mentioned, and he believed that its action was perfectly 

 satisfactory. 



He then drew attention to the causes of the variation of time in clocks, 

 which in his opinion was not to be attributed entirely to an alteration of 

 length in a part of the pendulum spring, but in some degree to a change in 

 the amount of elasticity in that spring, arising from a variation of tempera- 

 ture. The subject had been fully treated by Mr. Dent, in a paper read at 

 meetings of the British Association at Cambridge in 1833, and at Newcastle- 

 upon-Tyne in 1838. lie extended the inquiry to pendulums and succeeded 

 in separating and demonstrating the respective amounts of effect which 

 changes of temperature produced upon the elasticity of the spring and the 

 length of the rod. When the temperature was increased the clock lost, and 

 when a current of cold air was introduced the clock gained. By careful 

 analysis it had been shown, that of a loss of 12 seconds in a given time, SJ 

 seconds were attributable to the elongation of the rod, and the remaining 

 14 second to the decreased elasticity of the spring. His experience induced 

 him to recommend straight-grained split American deal as the best material 

 for pendulums. He found much difficulty in seasoning it. On one occasion 

 he had prepared some wood by partially exhausting the air, and boiling it 

 for three weeks in a mixture of turpentine and wax ; but even at the end of 

 that time air bubbles still rose to the surface. He had also tried boiling the 

 wood under pressure, but with the same result. He was induced to believe 

 that a very good pendulum could be constructed by a combination of a zinc 

 tube 1 inch diameter with a small steel rod. The expense would not be 

 considerable, and he thought the effect would be good. 



He approved of the proposed plan for adopting Greenwich mean time 

 generally throughout the kingdom ; in some lectures, delivered at the United 

 Service Museum in 1844, he had strongly insisted on the advantages of that 

 system, suggesting its being termed " British time." 



Mr. Brockedo.v suggested the possibility of some portion of the variation 

 being due to an enlargement of the diameter of the rod, from the increased 

 temperature, and thus opposing a greater surface to the air during its oscil- 

 lation ; this was in reality very slight, but with such delicate machinery as 

 clock-work the smallest causes produced unexpected results. 



Mr. IIoRNE stated that the weight used as a moving power, for well made 

 clocks, was generally too great, occasioning wear and destruction of the oil. 



He had a month-regulator, which had gone well for many years, with a 

 weight of only 6 lb. upon the train, which was equal to 1 i Ib.'upon an eight- 

 day clock. He was of opinion, that the power impinging on the pendulum 

 should be at, or very near to the point of suspension, so as to interfere as 

 little as possible with the natural gravitation of the bob, the principle which 

 is admitted as the most accurate for the admeasurement of intervals of time. 

 In making this statement he considered, that in the best kind of time-pieces 

 the pendulum spring should be entirely discarded, substituting a well har- 

 dened knife edge moving upon agate. 



Objections to keeping the same time at different places, 



Mr. Bidder believed that the general working of a line by London time 

 had been first introduced upon the Great Western Railway, and the effect 

 had been to oblige two clocks to be kept at the inns adjacent to the line — 

 one showing London time, and the other the correct time of the place. He 

 could not approve of the system proposed, as although it might be observed 

 correctly along the line, it would not be adopted in the tracts of country be- 

 tween the railways, and hence constant errors would occur. The errors 

 would be still aggravated by the London time differing both from the solar 

 time and the mean time of the various localities, lie thought, that the time 

 tables of railways should be calculated in accordance with the real mean 

 time, consistent with the longitude of the stations; then, by causing all the 

 railway clocks to be corrected, at given periods, by a person appointed for 

 the purpose, accuracy would be insured, without disturbing the present sys- 

 tem of local time. 



If the proposed system were applied to a railway of the length of those 

 on the continent, the difference of time between the two termini would be 

 immense, and the plan would disturb all existing arrangements as to time. 

 However the plan might be found to answer practically upon our compara- 

 tively short lines, it must not be supposed to be advocated by engineers for 

 more extensive lines. 



Mr. G. C. B. Curtis drew attention to the effect of an uniform time in 

 deranging all calculations as to tides ; if the proposed system was adopted, 

 an almanac would be required for every town. 



Mr. Walker could not agree with Mr. Bidder in the position he had taken 

 up. The proposal for keeping one uniform time was not applicable to coun- 

 tries whose great extent would render variation between the two extremities 

 of a Hne so great as to be objectionable ; the plan only applied to the rail- 

 ways in Great Britain, and upon them he must contend that the general 

 adoption of London time, for the periods of arrival and departure of the 

 trains, would induce a regularity which did not now exist. He was glad 

 when that plan was adopted on the Great Western Railway, as it showed 

 that the necessity for it was already felt. If the system was established on 

 all the railways, it would by degrees extend to the tract of country situated 

 between the lines, and even all the private clocks would have the two minute 

 hands showing the London time and that of the locality. As solar time had 

 been mentioned, it should not be forgotten that a difference now existed 

 between that and mean time, and that therefore no argument could be de- 

 duced from an aggravation of error, as regarded the time shown by the sun- 

 dials. 



At present, great discrepancies existed ; for instance, on the Great Western 

 Railway London time was observed along the Hne. On the London and 

 Birmingham Railway, he believed that at Birmingham, Liverpool time was 

 observed for trains going down and London time for trains going up ; so 

 that the passengers who stopped at Birmingham for a short time frequently 

 arrived at the station too late for the trains, relying upon their watches, 

 which had proved correct on the first part of the journey. 



Mr. Walker must still adhere to the opinion that for all except astrono- 

 mical purposes, London time might be advantageously adopted ; and even 

 where the tides were concerned ; because the difference of time on such a 

 limited extent as the coasts of Great Britain, could not be of any practical 

 disadvantage ; he thought that the recommendation of Mr. Vulliaray's paper 

 should be adopted, and he drew particular attention to the arrangement of 

 the hands on the dial, which was practically the same as that which had 

 been placed on Granton pier some time since ; but he thought it a great im- 

 provement in having one of the hands formed of the letters composing the 

 words " London time." 



Solar or true time, 



Mr. VuLLiAMY regretted having omitted in the paper all notice of solar 

 or true time. Formerly, when the use of clocks was very limited, and that 

 sun-dials supplied their place, solar time was constantly referred to, and the 

 best clocks were made with two minute hands, one with a sun at the end 

 indicating solar time, the other marking mean time. These machines were 

 called " equation clocks," because they showed the difference between solar 

 and mean time; they were, however, complicated, and consequently expensive ; 

 their great convenience consisted in the hand showing solar time, necessa- 

 rily agreeing with the time shown by the sun-dial. 



The ordinary equation tables indicated the difference between the time 

 shown by the two minute hands, which was constantly varying ; at certain 

 periods of the year the difference was only a few seconds, at others it was 

 upwards of li minutes; during part of the year the clock was "fast of the 

 sun," which was indicated by the hand showing mean time being in advance 

 of the hand showing the sun's time ; the remainder of the year the contrary 

 was the case. The sun-dial only showing the solar time, there was always an 



