TEINT. An artificial colour. TELEGRAPH. A machine as represented underneath, which serves to convey intelli gence by means of motions employed as the signs of words, by which a notice has been given 500 miles in three minuses,though the usual time would be 10 or 12 days. That such a means of quick communication at a distance 'was early in use is clear from the scene in the Greek play, in which a watehnssn from a tower in Greece and gives the informa tion that Troy was taken, adding have been looking out these ten years to see when that would happen, and this night it is done.' TELESCOPE An optical instrument composed of lenses, so situated as to bring re mete objects near to the view. It enables us so to dispose of the rays which proceed from distant objects, that we may see the image or spectrum formed in the focus of the object glass, very near, or under an increased angle. The angle of the image is as the focal length, or the distance from the object-glass to the image, and the angle at the eyeglass is as its distance from the image ; the magnifying power is, therefore, in the proportion of those angles. The glass nearest the object makes an image or picture by crossing and subse quently diverging rays, which a convex eye glass of short focus renders parallel for vision ; or which a concave eye-glass intercepts whale cohverging, and the image then proceeds di. reedy to the eye with parallel rays. In the figure annexed, the arrow is the object, the rays of which cross at the object-glass, and form an image which is viewed through a convex glass by the eye.
In the following figure 0 B is the object rays from which cress at G, in the object -gram A D, forming an image, which is viewed by E Y, the eyeglass, by the eye at H.
D object-glass, E concave eye-glass carrying paralleell rays to the eye.
The first and second are the common tele scope and microscope, the eyeglass being ,usually compounded of three eye-glasses to set the object erect ; and the third is the Gall. lean, or primitive telescope, and also the opera. glass, • The following is a section of the tubes, with the position of the object and eye glasses.
Telescopes are either refracting or reflect ing; the former consist of different lenses through which the objects are seen by rays re fracted by them to the eye, and the latter con sist of specula from which the rays are reflect-' ed and passed to the eye. The lens or glass turned to the object is called the object-glass, and that next to the eye the eye-glass, and, when the telescope consists of more than two lenses, all but that immediately next the object are called eye-glasses. Great ments have been made in the construction of telescopes, both reflecting and refracting. That constructed under, Dr.. Herschel's direction is the largest instrument of the kind, and pos sesses the highest magnifying power of any that was ever made. The tube of this telescope is thirty-nine feet four inches, it measures four feet ten inches, and every part of it is of iron that is rolled, or sheet iron, joined together by a kind of seaming, like the iron funnel of a stove. In order to command every altitude,
the point of support is moveable, and its metier is effected by the help of pulleys, so that it may be moved backward or forward and set to any altitude up to the very zenith. The tube is also made to rest with 'the point of support in a pivot, which permits it to be turned sidewise. A mounted telescope with rack-work for verti cal and horizontal motions, is represented by the engraving.
To whom we are indebted for the discovery of the powers of this instrument is not pre cisely known. Wolflus infers from a passage in the 'Magia Naturalis' of John Baptista Porta, that he was the first who made a tele scope, and this inference is the more probable, as Baptista Porta had particularly directed his attention to optical instruments ; but no certain mention is made of any telescope before 1590, thirty years afterwards, when a telescope six teen inches long was made and presented to Prince Maurice of Nassau, by a spectacle ma• ker of Middleburg, whose name is not exactly known,. being called Luppersheim, Jansen, and also No advances were, made in the construction of telescopes before the time of Galileo, who while at Venice acci dentally heard that a sort of optic glass was made in Holland, which brought distant ob jects nearer, and considering how this thing might be, lie set to work and ground two pieces of glass into a form, as well as he could, and fitted thein to the two ends of an organ pipe, with which he produced an effect that delighted and astonished all beholders. After ex hibiting the wonders of this invention to the Venetians on the top of the tower of St. Mark, he devoted himself wholly to the improving and perfecting the telescope, an which he was so successful that it has been usual to give him the honour of being the inventor. An anecdote mentioned by P. Mabillon in his travels, of having met, in a monastery of his own order, with a manuscript copy of the works of Com. mestor, written by one Conradus in the thir teenth century, and containing a portrait of Ptolemy looking through a tube at the stars, would seem to justify the supposition that this contrivance of facilitating the view of distant objects- was of earlier date than is generally considered ; but we are not informed whether the tube was furnished with glasses, and very probably tubes were then used to defend and direct the sight, and render the object more distinct by singling it from all other objects in the vicinity. It must not, however, be denied, that the optical principles upon which the effect of telescopes is founded are as old as Euclid at least, and wanted nothing but accident or reflec. tion to lead to this mode of applying them. TELLER. An officer of a Wrile who re ceives and pays money on checks.