849 



DRUMMOND, CAPTAIN THOMAS. 



DRUMMOND, WILLIAM. 



660 



Drummond had devised. Under his judicious advice the experiments 

 were prosecuted, and were rapidly attended with success : their 

 progress and results are detailed by the author in the ' Philosophical 

 Transactions' for 1826, as well as the first application of the lamp to 

 actual use in Ireland. When a station, Slieve Suaught, in Donegal, 

 had long in vain been looked for from Davis Mountain, near Belfast, 

 the distance being sixty-six miles and passing across the haze of Lough 

 Neagb, Mr. Drummond took the lamp and a small party to Slieve 

 Snaught, and by calculation succeeded so well in directing the axis of 

 the reflector to the instrument, that the light was seen, and its first 

 appearance will long be remembered by those who witnessed it. The 

 night was dark and cloudless, the mountain and the camp were covered 

 with snow, and a cold wind made the duty of observing no enviable 

 task. The light was to be exhibited at a given hour, and to guide the 

 observer, one of the lamps formerly used, an argand in a lighthouse 

 reflector, was placed on the tower of Randalstown church, which hap- 

 pened to be nearly in the line at fifteen miles. The time approached 

 and passed, and the observer had quitted the telescope, when the 

 sentry cried, " The light ! " and the light indeed burst into view, a 

 steady blaze of surpassing splendour, which completely effaced the 

 much nearer guiding beacon. 



An apparatus invented by Colonel Colby, consisting of flat plates of 

 polished tin, at angles calculated to reflect the sun's rays in the 

 required direction, was resorted to, and with entire success. It was 

 however somewhat elaborate ; because, from the rapid motion of the 

 sun, or rather of the earth, in its orbit, the same pole and set of plates 

 would only answer for a single station, and for a short time on a very 

 few days ; the principle however was now obvious, and the elements 

 which had been called into play soon suggested the more perfect 

 instrument. Fiom a calculation, of which the variables were the 

 relative position of two stations and that of the sun, a happy step led 

 to an instrument by which the problem should be as it were solved 

 by construction a telescope in the line between the objects, connected 

 with one to be directed on the sun and carrying u mirror: such 

 accordingly was the first helioatat of Drummond ; its mechanism is 

 described in the paper already referred to (' Phil. Trans.,' 1826), and, 

 like the lamp, it was used successfully in the first season of the 

 trigonometrical operations in Ireland. It was originally intended to 

 give this instrument a divided circle, by which its direction could be 

 fixed ; but as this was not effected, a theodolite was necessary in con- 

 junction with it, and practice soon showed that if a theodolite were 

 used, a more simple and less costly heliostat might be adopted. This 

 accordingly was devised by Mr. Drummond before the second season ; 

 the direction being effected entirely by the theodolite, instead of being 

 as before dependent partly on the theodolite and partly on the adjust- 

 ments of the heliostat. The telescope of the heliostat now became 

 useless, and it remained a simple mirror moveable in two directions, 

 that is, on a horizontal and on a vertical axis, of which the light was 

 guided by a directing staff previously placed by aid of the theodolite. 

 This instrument proved so satisfactory that it has ever since remained 

 in the form adopted on the survey, and it is every season found more 

 and more useful. By its aid several observations have been made at 

 distances exceeding one hundred miles ; and such is its facility of 

 direction owing also no doubt in some degree to the great divergenca 

 which even the best mirrors give to reflected light that the theodolite 

 is now frequently dispensed with, and by a few simple distances and 

 measurements computed beforehand, a single soldier is sent with a 

 heliostat to some remote mountain or island, with tolerable certainty that 

 his reflection will be seen as soon as the sun shines after he reaches it. 



Mr. Drummoud's original heliostat was not completed till 1825. A 

 heliostat h&d also been invented by Professor Gauss, of Gottingen, in 

 the process of a survey carried on by him. in Hanover. A very simple 

 one had also been used by the late Commander Mudge, of the Royal 

 Navy, while surveying on the coast of Africa in 1823-24, which con- 

 sisted merely of a sextant sent forward to the station to be observed, 

 and so adjusted as to throw the sun's light to the observer. 



In the autumn of 1824 Colonel Colby made a general reconnaissance 

 of Ireland for the purpose of fixing on the mode of survey, the choice 

 of stations for the great triangulatiou, and the most fitting place for a 

 b;ise. He selected Mr. Drummond to accompany him on this tour. 

 The Plain of Magilligan was chosen, and Colonel Colby's attention was 

 next directed to a fitting apparatus for the measurement. 



Colonel Colby's long experience had shown him the defects of the 

 apparatus formerly employed, and he boldly devised one altogether 

 new, in which compensating expansions were to be used to form an 

 unalterable linear measure. The construction of the instruments 

 required long and careful experiments, the charge of which was con- 

 fided to Mr. Urummond ; and so far as was necessary to prepare the 

 instruments for use in the field, they were performed by him or under 

 his direction. It occurred to him that mica, which had then recently 

 been recommended by Sir David Brewster for pendulum rods, might 

 be applicable to this new purpose. Colonel Colby allowed experi- 

 ments to be tried on that substance, but they were not satisfactory, 

 mid Mr. Drummond abandoned the idea. The apparatus was com- 

 pleted according to Colonel Colby's original plan, and successfully 

 used in the base at Magilligan. In the measurement Mr. Drummond 

 was again employed, and whenever Colonel Colby was absent on other 

 duty the charge of the operations devolved upon him. 



ciou. DIV. VOL. n. 



At this period of invention and improvement which preceded the 

 commencement of the survey of Ireland, Mr. Drummond gave some 

 consideration to the barometer, an iustrument even now susceptible 

 of improvement, but which had not then received so much attention 

 as it has since. His favourite construction was the siphon, and he 

 made one with his own hands, which performed remarkably well ; but 

 he was not in possession of various modes of reading which have since 

 been used : and he devised a singular mode of bisecting a reflected 

 image of the surface a ghost, as he called it ; but he arrived at no 

 permanent or practical result, and at length abandoned the subject 

 from a conviction, to use his own words, that the errors to which the 

 barometer was liable from causes beyond control, were greater than 

 the quantities he had been dealing with. His researches on light, and 

 his intimacy with Professor Leslie, led him to the use of the photo- 

 meter, the aethroscope, and other philosophical instruments of more 

 or less practical utility among others, Wollaston's thermo-barometer ; 

 indeed, at this period so active was his mind and so constant his 

 application, that scarcely an instrument existed that he did not examine 

 and consider, with a view to render it useful for the purposes of the 

 survey; and the elaborate collection with which the meteorological 

 observatory on Divis was furnished, presented a singular spectacle on 

 the mountain-top. He carefully made observations and recorded them, 

 till a calamitous storm destroyed the observatory and all its contents 

 together. 



A severe illness which Mr. Drummond contracted from exposure 

 during the Irish survey compelled him to return to Edinburgh, where 

 he was unable to devote himself to study, but he had taken much 

 pains to perfect his light, and he now began to revert to the idea 

 that he had early formed of adapting it to lighthouses. In this he 

 was liberally met by the corporation of Trinity-house, and to it he 

 devoted much of his time during the following winters : the experi- 

 ments he made, with their success, are detailed in the ' Philosophical 

 Transactions' for 1830. The corporation of Trinity-house placed at 

 his disposal a small lighthouse at Purfleet ; and the brilliant effect of 

 the light as seen from Blackwall, where at a distance of ten miles, it 

 was sufficiently strong to cast shadows, made it an object of very 

 general interest. With regard to his share in the application it may 

 be proper to remark, that Mr. Drummond' s merit was in rendering 

 practically useful a recondite experiment, by devising a means of 

 procuring and using without danger agents so turbulent as the mixed 

 gases, making the apparatus sufficiently portable and simple to be 

 employed in the circumstances of exposure required for the survey, 

 and, perhaps more than all, for the happy idea of using this minute 

 spherule of concentrated light as the radiating focus of a parabolic 

 mirror. But the original object of the lamp, its application to light- 

 houses, presents difficulties which have yet to be overcome. The abstrac- 

 tion of Mr. Drummond's attention at the moment when he was nearest 

 to success, must, so far as the light is concerned, be considered matter 

 of regret. 



Mr. Drummond was employed to superintend the very laborious 

 operations necessary to the perfecting the schedules and laying down 

 tha boundaries to the old and the new boroughs under the provisions of 

 the Reform Bill. Mr. Drummoud was appointed to this commission 

 on the recommendation of Lord Brougham, not however without 

 some severe opposition from one of his colleagues, who doubted much 

 as to the propriety of putting at the head of so important a depart- 

 ment a young lieutenant of the Engineers. He however more than 

 justified the expectation formed by his patron. 



When the Reform Bill was passed, Mr. Drummond returned to his 

 duties on the survey, and he had made preparation for giving an 

 account of the base before adverted to, when he was again called into 

 public life by being appointed Lord Spencer's private secretary. On 

 the dissolution of tho government he received a pension of 3001. a 

 year, obtained for him by Lord Brougham, his constant friend. 



In 1835 he was made under-secretary for Ireland; he much dis- 

 tinguished himself in the report on railways iu Ireland, being at the 

 head of the commission. We shall not attempt to trace his labours 

 as a politician or on the railway commission, but his talents and 

 assiduity were admitted by all, even his strongest political opponents. 

 He laboured incessantly at his duties, and probably hastened his death 

 by his continued application. This took place April 15, 1840, " in 

 the plenitude of mental power and maturity of knowledge, beloved in 

 private and esteemed in public." Soon after his death there was a 

 subscription for a statue, which was executed at Rome, and erected 

 in Dublin. 



DRUMMOND, WILLIAM, the son of Sir William Drummond of 

 Hawthornden, was born December 13, 1585. He was educated at 

 Edinburgh, and studied civil law in France. On his father's death in 

 1610, he relinquished -his profession and devoted himself to literary 

 pursuits at his.paternal mansion of Hawthorn Jen. He did not however 

 experience that freedom from trials which he had probably anticipated 

 in his retirement. His betrothed bride died on the ove of their 

 marriage ; and iu order to divert his thoughts from brooding over 

 this deep and bitter affliction, he undertook a tour which lasted eight 

 years, during which time he visited Germany, France, and Italy, and 

 collected a library of great value, of which part is now in tho pos- 

 session of the University of Edinburgh. In his forty-fifth year ho 

 married a lady whose fancied likeness to the former object of his 



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