attentive, and obliging, in all the relations of life; and he was most warmly loved by all who knew him best. It is probable that intense application to his labours laid the foundation of the disease-consumption of the lungs-of which he died. The symptoms of the fatal malady began to manifest themselves in the autumn of 1836; but he was able to continue at work, although with many interruptions, until within two or three months of his death, which happened on the 15th January 1838. Throughout the whole of his illness, he maintained the same meek and quiet deportment which ever distinguished him. He spoke little; but that little proved how much his spirit was cheered by Christian faith and hope, and discovered on what a deep foundation were based the remarkable humility, simplicity, and sincerity, which formed the chief ornaments of his character, and endeared him to all connected with him. MARCH 30. 1844. Description of Portable Levelling Instruments. By DAVID STEVENSON, F.R.S.E., F.R.S.S.A., Civil Engineer, Edinburgh. Communicated by the Royal Scottish Society of Arts. With a Plate. In examining a tract of country, I have often experienced the want of some portable, and, at the same time, accurate instrument, for ascertaining, in a general manner, the relative levels of different points, previous to determining the line of a more detailed survey. A small spirit-level without any telescope, having a common sight and cross-hair attached, is sometimes used for that purpose, being fixed on a staff stuck into the ground. The large instruments commonly used in levelling are also often employed, but neither of these instruments answers the object I had in view; the first being much too rude for the required accuracy, and the second too • Read before the Society, 12th February 1844. heavy for easy transport. The level represented in the accompanying drawing (Plate 1st), was designed to supply this want. It consists of an accurate spirit-level, a 10-inch telescope, and a compass, so arranged as to admit of being very portable. The telescope unscrews at letter A, so as to form two compartments, and the whole is packed in a pocket case measuring 6 by 23 inches; and the tripod on which it stands does not exceed the bulk of a thick walking staff. Referring to the drawing, B C is the level, D a circular level, E the compass, F screw for adjusting focus, G the eye piece, H screw acting on spring K L, which is fixed to the telescope at M by a crutch on which it moves, N the screw by which it is fixed to the tripod, O P Q R the top of the tripod, which contains a ball and socket-joint, shewn in dotted lines, which can be clamped and unclamped by means of a screw wrought on the inside of the part S T. In setting the instrument, the screw S T is first unclamped, and the instrument is moved by the hand on the ball and socket-joint until the air-bubble of the level D occupies the centre of the circular box containing it. The screw S T is then clamped, and the instrument being directed to the object to be observed, the final and more perfect adjustment is made by bringing the air-bubble B C to occupy the centre of its tube, which is done by means of the screw H, which acts on the spring K L. The tripod is that used by Dollond for the camera lucida, and answers both instruments. The telescope can be made either, as in órdinary levels, to reverse the objects, or, as in theodolites, to shew them in their true positions. In this level made for myself, I have adopted the latter construction, in order that the instrument may answer more perfectly the purposes of a field telescope. The addition of the compass is also a further convenience. In connection with this instrument, I have also had a portable levelling staff made, which also is shewn in Plate I. It consists of an elliptically-moulded staff, 3 ft. 3 in. in length, and cut through the middle; the two halves are hinged at one extremity, and when unfolded, are fixed by a spring at A, forming a rod 6 ft. 6 in. long, on the flat side of which the graduations of feet and inches are painted; when closed, the gradua Edin New Phil. Journal. Fol. XXXVII Plate IPage 100 rs Small portable Levelling Instrument & Rod, constructed by Mess.Adic for David Stevenson.C.E tion is protected from injury, and the whole forms a convenient walking staff. These instruments, which were made for me by Messrs Adie of Edinburgh, I have found very convenient; and, I am persuaded, they will be suitable in all circumstances where the combination of accuracy and portability is required. DAVID STEVENSON. EDINBURGH, 11th January 1844. Some Account of Levelling Instruments, with Description of one of an Improved Form. By THOMAS STEVENSON, Civil Engineer, Edinburgh. Communicated by the Royal Scottish Society of Arts.* The improved spirit level about to be described, was made for me in 1810 by Mr Adie, and afterwards described in a letter to the Institution of Civil Engineers.+ Since then I have had two levels of the common construction altered to the new form. On a late occasion these instruments were exhibited to the Royal Scottish Society of Arts; and as no drawings had been laid before the public, that Society requested me to prepare a description with diagrams, that these might be published in their Transactions. In accordance with their request, therefore, I have drawn up the present description; and have also consulted many early writers, to ascertain, as well as I could, the history of one of the most important of geodetical and engineering instruments. There unfortunately exists a great deal of conflicting evidence regarding the true inventors of the different parts of the spirit-level. Indeed, there are hardly two authorities who agree upon the subject. The great Huygens appears to have been the first to apply the telescope to a level of his, which was constructed on the principle of the plummet. This is noticed, in the life pre * Exhibited and verbally described to the Society on 22d January 1844; and this written description requested. + Engineer and Architect's Journal, vol. v. |