188 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Junk, 



frequently objectionable from the same cause, and he maintained that they 

 should never be llius applied, but only as pictures wilhin frames, if applied 

 at all. 



The effect of linear and aerial perspective was adverted to, and the 

 softcninj; influences of colour in aerial perspective were dencribed as per- 

 taining to the highest order of artistic talent. .Scenes of this kind are com- 

 posed of a number of parts, the Hats representing sky and extreme dis- 

 tance, while tlie middle distance an<l foreground are broken into perspec- 

 tive forms. Float-lights being placed beliind these parts, impart bnlliaat 

 effects that no colouring can attain to, resembling tiie sunny spots of a 

 landscape. 



Linear perspective required, it was said, very great consideration, and 

 failures in street architecture, and similar sulyects, are often evident to the 

 least initiated observer. The artist, hov^'ever, has to contend with serious 

 disadvantages from not being permitted to set out this class of scenes upon 

 the stage instead of in the painting-room ; and the manner in which they 

 are produced ought to be borne in mind when judging of their merits. 

 htreet architecture offers a peculiar difficulty f'om the actors influencing 

 the scale by their comparative size ; this illustrates the great absurdity of 

 placing a facade of tlie National Gallery or other well-known building 

 within the area of a theatrical scene, without a proper regard to distance. 

 As an instance of a favourable effect, he named a scene in the " School for 

 Scheming," at the Haymarket, representing portions of streets abutting on 

 the quay st Boulogne, which he considered far removed from a common- 

 place effe„ l.^nd that it also testified what might be obtained by placing 

 scenery obliquely 



Mr. Dwyer next alluded to the taste and refinement Madame Vestris 

 had first presented to the public in her dr^iwing-room scenes, elegantly and 

 completely furnished ; and he also mentioned with commendation some 

 interiors produced at the Haymarket, in a similar spirit. He admired 

 this perfect kind of representation, ami was pleased with the manner in 

 which it had been extended to exteriors, garden scenes, &c., and he re- 

 ferred to the garden scene in the " Lady of Lyons," at Sadler's Wells, in 

 which the stage is covered with a painted cloth iniitaiive of gravel walks, 

 grass plots, shrubberies, &c., producing together a very superior effect. In 

 a snow scene in the " Battle of Life," at the Lyceum, the siage was co- 

 vered with painted canvas very successfully, and in the " Flowers of the 

 Forest," the scene of a village church, with well-worn paths, &c., simi- 

 larly treated, was equally skilful and pleasing. 



Mr. Dwyer commented upon the fits and starts usual to these matters, 

 stating that the betier scenes were exceptions, while the imperfect school 

 retained the pred<iminance. As one of the earliest and most perfect illu- 

 sions ever depicted, he described a scene introduced in the opera of " Acis 

 and Galatea." The last scene in the ballet of " Coralia," at her Majesty's 

 Theatre, was also fully described, as an eminent example of scenic dis- 

 play. 



The author then noticed the machinery pertaining to theatres, and re- 

 commended the use of painted canvas placed on rollers sullicienlly lofty so 

 as to dispense with the series of curved, scolloped, and straight fly borders, 

 ordinarily representing sky, &c. He next reviewed the inconsistencies 

 which occur in scenery and properties being of a different period in cha- 

 racter and stvle to that of historical dramas, mentioning a scene in " Lucia 

 de Lammermoor," at the Italian Opera House, C'ovent Garden. It repre- 

 sents a Norman interior furnished with one chair of modern French style, 

 and a table of douhiful period, the slory of the opera being in IG69. He 

 contended that those adjuncts are imponant; and that if costume, man- 

 ners, and customs are rendered faithfully, properties should receive equal 

 attention. The pmgress in matters of costume from the time of Garrick 

 was noticed, and the properties introduced by John Kenihle, I'lanch*;, and 

 others, were mentioned with encomiums. The increasing taste of actors, 

 shown in careful dressing and wearing apparel Hith a bearing in accord- 

 ance with the period represented, was also favourably commended, as 

 displaying research and accurate stmly of their art. Mr. Uwyer drew 

 attention to the force with which the varieties of colours in dresses may 

 be developed, by having regard to the background and to the position of 

 the actors. An acknowledgment was made of the elevated tasteand artistic 

 arrangements which Mr. Macready had frequently shown in groupings 

 and tableaux, and he concluded with the expression of a desire to find a 

 proper ftelmg more generally established between the artists, actors, and 

 managers, so that the capabilities of combined talents might produce 

 results at once gratifying, elevating, and promotive of the welfare of the 

 arts. 



INSTITUTION OF CIVIL ENGINEEfiS. 



April 27. — Sir J. Renme, President, in the Chair. 



" On the laws of Isochruntsm of the BitlancfSpring as connected with the 

 higher order uj adjustments of Watches and Lhrunumeters." By Mr. C 

 Froosiiam. 



The first portion of the paper gave an historical sketch of the horologiral 

 inventions and writings of the artists of the eighteenth century ; w hich ap- 

 pear to constitute the basis of all the knowledge possessed in the present 

 day, and the principles of whose school were still followed in the construc- 



tion of both watches and chronometers of the better sort. It was admitted 

 that, by the aid of machinery, and the practical skill of the workmen, the 

 separate pieces of clocks and Matches are now produced in a high state of 

 perfectiim ; liut it was contended, that horology, as a science, had declined 

 since the days of Hooke, Bernouilli, Sully, Graham. Harrison, Camus, 

 Mudge, Ellicot, the two Arnolds, Karnshaw, Le Roy, Berlhoud, and oiliers, 

 whose splendid talents and scientific attainments were all devoted to the 

 elevation of the art of constructing timekeepers. Among these Dr. Hooke 

 appears to have been the first to bring the forre of acute reasoning and pure 

 mechanical genius to bear upon the practice of the art, aud from his experi- 

 ments upon the pendulum and the appli< ation of the balance-spring — which 

 latter unquestionably laid the foiindaiioii of the chrouometric art — it is 

 evident that he partially r.ii»ed the veil which concealed the laws of the 

 isochronism of the spiral spring; as is demonstrated by his expression 

 " «/ tensia sic ris," — and it is extraordinary that so plain a hint was not 

 immediaiely seized on by the able men who succeeded him. — .\rnold ap- 

 pears to have been the first who really practically comprehended the sub- 

 ject ; and in the course of his researches he invented the cylindrical spring 

 and compensation-balance, which formed the commencement of a new era 

 in the science. The merit of the discovery of the isoi hrunism in France 

 was contested by Le Koy and Berlhoud. Bernouilli noticed, in a paper 

 read to the Acndemie in 1747, the f.ict of the loss of elastic force in balance- 

 springs, from exposure to heat ; and the experiments of Berlhoud demon- 

 strated that in passing from 32° to 92° Fahrenheit the loss per diem was 

 6 minutes 33 seconds. 



The paper then considered generally the subject of the isochronism of 

 the balance spring, enunciating isochronism to be an inherent property of 

 the balance-spring, depending entirely upon the ratio of the spring's ten- 

 sion following the proportion of the arcs of infiection : a balance-spring, 

 therefore, having the progression required by the law of isochronism will 

 preserve that property, whether it be applied to a balance making quick or 

 slow vibrations. Tlie elastic force of balance-springs was considered as a 

 constant, because the aciion is by a number of consecutive impulses follow- 

 ing each other in such rapid succession as to constitute an uniaterrupled 

 and continuous force. This is shown in considering ilie accelerated and 

 retarded motion of the balance, when by following it through an entire arc 

 of vibration, it will be seen that if the balance be moved over a given num- 

 ber of degrees, the spring will be wouud into a certain tension, and has 

 acquired a certain elastic force due to the angle over which it is inflected. 

 Tins elastic force being then transferred to the balance, it will be exerted 

 in overcoming its inertia ; and at the expiration of the first period will have 

 communicated a slight motion to it. During the next period, its slate will 

 be tlial of comparative and not absolute inertia (for it decreases as the mo- 

 tion increases), whence it follows that as the spring's force is exerted against 

 a body in motion instead of at rest, it will necessarily accelerate progres- 

 sively the motion the balance had previously acquired, until the spring 

 arrives at the point of quiescence, where, having lost all its elasticity, it 

 ceases further to urge the balance, and a new relation of power and resistance 

 lakes place. The spring's force being transferred to the balance, it assumes 

 a new character, has acquired siilbcient momentum to carry it through the 

 second half of the v ibratmn, aud to inflect the spring over an angle equal to 

 that first passed over, and to give it the requisite tension to comnieuce a 

 new vibration,— parlicularly as during the second half of the vibr^iliou the 

 spring has so little tension that its foice retards but sli:;htly the motion of 

 the balance. After much acute reasoning upon this position, illustrated by 

 numerical examples, the author proceeded to descritje the liebcal and the 

 flat-coiled springs which are used in chroiioineters and watches, and the 

 manner of regulating llieir aciion, so as to take advantage of the isoLhrouism, 

 inslancing the advautages to be derived from the innate power po.-,sessed by 

 an isochronal-spring of resisting the iuOueiic es which cause a change of 

 rate — such as change of position, increased friction from dirt, or the viscidity 

 of the oil at low leiiiperature This was illustrated by an example of three 

 balls falling in equal times through spaces regulated by the densities of the 

 medium, viz., in vacuo, iu air, and lu water, wherein they traierse spaces 

 equal to the squares of the times. — So, it was argued, it was with increased 

 friction in watch work; for the elastic forces of the balance-spring being 

 constantly proportional to the angle of iufieetioo, whatever was the amount 

 of friction, the law of isochronism remained unchanged ; aud trittioii was 

 only an adventitious circumstance, which allccts the eiteut of the arc of 

 vibratiou, but not the time of its description. 



Mai/ 4. — The discussion upon the aliove paper was continued. The vis- 

 cidity of the oil, from its nature and from external causes, and tlie had effects 

 arising from it, were dwelt upon at great length ; hut, it did not appear, that 

 either chemistry, or the practical experience of working watth-makers, had 

 as yet either pointed out the true causes of viscidity, or enabled its effects to 

 be satisfactorily remedied. The relative values of various modes of trial of 

 timekeepers were also dilated upon. It was attemjited to be shown, but 

 was successfully refuted, that a taper spring would produce the same effect 

 as the isochronal arrangement, and that the tapering could be effected by 

 machinery. Among the external influences affecting the oil in time-keepers, 

 was mentioned the circumstance of the watches belonging to George IU., 

 wliich, being kept in drawer of cedar wood, soon stopped, and it was found 

 that the oil had changed into a substance resembling gum. Attempts had 

 been made to substitute oil of sweet almonds for olive oil, on the recom- 

 mendation of a distinguished chemist, hut they were signal failures. The 

 inefficiency of the remoutoir movement was clearly shown, although its in- 



