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letter written in his hut on the night of November 11, 1825. In the moment of success his first thought was to communicate the pleasure of it to his beloved mother:

“SLIEVE SNAGHT,

Friday night, Nov. 11, 1825. “MY DEAR MOTHER,—What has become of Tom ? and why does he not write ? are questions which you may of late have not unfrequently asked, and, I dare say, without any one being able to give a very satisfactory answer. Why, then, I am perched upon the top of Slieve Snaght (the Snowy Mountain), 2100 feet high in the centre of Innishowen, the wildest district in Ireland. Since the 23d of August, when a pole was placed on this hill, we have endeavoured to observe it from Divis, near Belfast, on which our tent was placed, but in vain. Constituting an important point in the triangulation of Ireland, our sojourning on the hill-tops has been prolonged to an unusually late period, in the daily hope that it would have been visible. Disappointment, however, was our lot, and the weather becoming broken and tempestuous, the colonel determined upon breaking up the camp and retiring to winter quarters. Just at that moment a letter was received from one of our officers encamped on Knock Layd, a hill about 40 miles distant, giving a splendid description of the solar reflection which I had exhibited to him, and which had been seen through a very hazy atmosphere, and seen for a time with the naked eye; and one of our officers tells me that the country people, whom curiosity had attracted to the spot on hearing the distance at which it was placed, actually raised a shout of exultation at its brilliant appearance. This being known at Divis, it became a question whether Slieve Snaght should be atteinpted at this season; and after due deliberation, it being decided that it should, I made a forced march upon this place, and, leaving Belfast on Tuesday forenoon, slept on this mountain on Thursday night, the 27th October, our tents erected, and hut constructed, and all the apparatus of the lamp ready for work. For the first week our life was a struggle with tempest-our tents blown down, our instruments narrowly escaping, and ourselves nearly exhausted. At length, by great exertions, we got two huts erected, one for the seven men who are with me, the other for me a lonely and humble dwelling, it is true, and now that the snow has fallen, so completely covered up that it is not very easily distinguished; nevertheless affording good shelter, warm and comfortable, and, at the present moment, with a good peat fire. The weather at length improved, and Wednesday the 9th instant brought our exertions to a successful termination. The colonel, after making the necessary arrangements, took his departure for London on the very day I arrived here, leaving Murphy and Henderson to keep a constant look-out for the lights. Their assiduity has been unremitting, and their fatigue by incessant watching not a little. This day brought me a letter from Murphy, which begins thus: “Your light has been most brilliant to-night for three hours and twenty minutes, as was your solar reflection to-day. I began by giving you the pleasing intelligence in a condensed form, but now I must most heartily congratulate you, my dear friend, on the complete success which has thus crowned your very ingenious and laborious exertions for the good of the service. I trust they may eventually prove as beneficial to yourself. I really feel sincere pleasure in making you this communication. I will now give you some details. I first had notice of your appearance from Elliot, who called out that he saw the light, and in fact, though five times more remote, you were much brighter and larger than the Randal's tower reflector.' I have given you a long extract, because I think it will interest and please you. I have only to inform you now that the distance in a straight line between the two places is about 67 miles. I had a letter from the colonel to-day in London, very anxious to know the result of our labours. To-morrow I commence my retreat; on Monday I shall be in Derry, where I shall have to remain a day. .... From Derry I proceed to Belfast, where I shall be detained two or three days, and then I make direct for Edinburgh. At Belfast I entreat you to let me hear from you, and I am anxious to hear how Eliza bore the journey from Callendar, and how

the house is. My last intelligence is her own letter, which I received about the 19th ultimo, on the evening succeeding a gale of wind, which overthrew two of our marquees, and set fire to our cooking-house. I have written you, my dear mother, a long and gossipping letter, and it being now three o'clock in the morning, it is fit that I should stop. To John and Eliza my kindest love, and to Eliza my best thanks for her kind letter. It may amuse my aunt to read this letter to her, and tell her that I add my best regards.—And now, my dear mother, believe me your affectionate son,

“T. DRUMMOND.”

CO

This chapter, composed mainly of quotations, must be concluded by another from the Memoir of General Larcom :.

“The triumphant success which attended the lamp and heliostat at the close of 1825, was purchased at the cost of a severe illness. A mountain camp, at an altitude of two thousand feet in the winter of these climates, is, under any circumstances, a severe trial; but Drummond and his little party were peculiarly exposed. Few in number—being merely detached from the general camp at Divis—they were ill able to buffet with the storms of these wild regions; and the tents were so frequently blown down, that after the first few days they abandoned them, and constructed huts of rough stones, filling the interstices with turf. Such, without the additional luxury of a marquee lining, was the study and laboratory on which depended the success of the new instruments. Here were to be perforined the delicate manipulations their adjustment required. Here was to be manufactured the oxygen destined for the portable gasometer ; and, cowering over the fire, or wrapped in a pilot coat, was Drummond day and night at work. A frame and system attenuated by fatigue and excitement were ill able to bear up against such exposure. He struggled to the last ; but no sooner had his efforts been crowned with success than he sank, and a severe illness compelled him to return to Edinburgh, to the care of his family and friends."

CHAPTER VIII.

SURVEY OPERATIONS, 1826-1828 ; SIMPLIFIED FORM OF

THE HELIOSTAT; THE MEASURING BARS ; THE BASE AT LOUGH FOYLE.

The period of invention and improvement which preceded the commencement of the Irish Survey had other results besides those which have been described. To procure apparatus which would secure rapidity and accuracy in the work of the great triangulation, was not the only object in view. It was designed that the Irish Survey should be a more general Survey than any that had yet been made ; should embrace not only geodetical facts, but also facts meteorological and topographical. The Engineer officers were becoming good physicists as well as good surveyors, and, while discharging their more immediate duties, were in various ways promoting the interests of science. The topographical department grew in importance as the work of the Survey proceeded. It owed most in the course of its development to General Larcom, who possessed special qualifications for advancing this branch. He unites literary and antiquarian tastes with an aptitude at once for science and for the work of administration. The department which Drummond created and fostered was that of meteorology.

During the period of preparation scarcely an instrument existed which Drummond did not consider with

a view to rendering it useful in the Survey; and for him to consider an instrument was to attempt to improve it. He long tried to improve the barometer. His favourite construction was the syphon, and he made one with his own hands which performed remarkably well. In the course of his experiments, he devised a singular mode of bisecting a reflected image of the surface—a ghost, as he called it; but it did not help him to any practical result. He at length, says General Larcom, 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.”

The elaborate collection of instruments which he brought together in the meteorological observatory on Divis—the first Irish station is said to have presented a singular spectacle on the mountain top. He carefully observed and recorded them, till the observatory was destroyed by a calamitous storm.* “The season on Divis,” says Colonel Portlock, "was indeed a noble one. The camp became a school not merely of geodetical but of meteorological science. And though the difficulty of moving the delicate instruments from hill to hill, and preserving them from injury amidst the mountain storms, obliged Colonel Colby to abandon the use of some of them in subsequent stations, enough were retained to add the skill of practice to the theoretical knowledge which had been acquired at that first and most instructive station.” It is characteristic of Colonel Portlock that he should say not one word of Mr Drummond in connection with this “noble season” and “most instructive station.” He gives the whole credit to “ the chief,” and has none for the projector and creator of the

* The Larcom Memoir, p. 6.

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