By G.E. LUMSDEN.
These are the palmiest days in the eventful history of physical and observational astronomy. Along the whole line of professional and amateur observation substantial progress is being made, but in certain new directions, and in some old ones, too, the advance is very rapid. As never before, public interest is alive to the attractions and value of the work of astronomers. The science itself now appeals to a constituency of students and readers daily increasing in numbers and importance. Evidence of this gratifying fact is easily obtained. There is at the libraries an ever-growing demand for standard astronomical works, some of them by no means intended to be of a purely popular character. Some of the most influential and conservative magazines on both sides of the Atlantic now find it to be in their interest to devote pages of space to the careful discussion of new theories, or to the results of the latest work of professional observers. Even the daily press in some cities has caught the infection, if infection it may be called.
There are in New York, Philadelphia, St. Louis, and other centers of population on this continent leading newspapers which, every week or so, publish columns of original matter contributed by writers evidently able to place before their readers in an attractive form articles dealing accurately, and yet in a popular vein, with the many-sided subject of astronomy. In scientific matters generally, there is abroad in this and other countries a spirit of inquiry, never more apparent than at the present time.
Readers and thinkers may, no doubt, be numbered by thousands. So far, however, as astronomy is concerned, the majority of readers and thinkers is composed of non-observers, most of whom believe they must be content with studying the theoretical side of the subject only. They labor under the false impression that unless they have telescopes of large aperture and other costly apparatus, the pleasures attaching to practical work are denied them. The great observatories, to which every intelligent eye is directed, are, in a measure, though innocently enough, responsible for this. Anticipation is ever on tiptoe. People are naturally awaiting the latest news from the giant refracting and reflecting telescopes of the day. Under these circumstances, it may be that the services rendered, and capable of being rendered, to science by smaller apertures may be overlooked, and, therefore, I ask to be permitted to put in a modest plea for the common telescope. What little I shall have to say will be addressed to you more for the purpose of arousing interest in the subject than for communicating to you any information of a novel or special character.
When making use of the term "common telescope," I would like to be understood as referring to good refractors with object glasses not exceeding three or three and one-half inches in diameter. In some works on the subject telescopes as large as five inches or even five and one-half inches are included in the description "common," but instruments of such apertures are not so frequently met with in this country as to justify the classing of them with smaller ones, and, perhaps, for my purpose, it is well that such is the fact, for the expense connected with the purchase of first rate telescopes increases very rapidly in proportion to the size of the object glass, and soon becomes a serious matter. Should ever the larger apertures become numerous on this continent, let us hope it shall be found to have been as one of the results of societies like this, striving to make more popular the study of astronomy.
It is not by any means proposed to inflict upon you a history of the telescope, but your indulgence is asked for a few moments while reference is made to one or two matters connected with its invention, or, rather, its accidental discovery and subsequent improvement.
The opening years of the seventeenth century found the world without a telescope, or, at least, such an instrument as was adapted for astronomical work. It is true that long years before, Arabian and some other eastern astronomers, for the purpose, possibly, of enabling them to concentrate their gaze upon celestial objects and follow their motions, had been accustomed to use a kind of tube consisting of a long cylinder without glasses of any kind and open at both ends. For magnifying purposes, this tube was of no value. Still, it must have been of some kind of service, or else the first telescopes, as constructed by the spectacle makers, who had stumbled upon the principle involved, were exceedingly sorry affairs, for, soon after their introduction, the illustrious Kepler, in his work on "Optics," recommended the employment of plain apertures, without lenses, because they were superior to the telescope on account of their freedom from refraction.
But as soon as the principle by which distant objects could, apparently, be brought nearer the eye became known and its value recognized by philosophers, telescopes ceased to be regarded as toys, and underwent material improvements in the hands of such men as Galilei, and, later, even of Kepler himself, Cassini, Huyghens, and others. Galilei's first telescope magnified but three times, and his best not much above thirty times. If I comprehend aright what has been written upon the subject, I am justified in saying that this little instrument in my hand, with an aperture of one inch and one-quarter, and a focus, with an astronomical eye-piece, of about ten inches, is a better magnifier than was Galilei's best. With it I can see the moons of Jupiter, some spots on the sun, the phases of Venus, the composition, in some places, of the Milky Way, the seas, the valleys, the mountains, and, when in bold relief upon the terminator, even some of the craters and cones of the moon. Indeed, I am of opinion I can see even more than he could, for I can readily make out a considerable portion of the Great Nebula in Orion, some double stars, and enough of the Saturnian system to discern the disk of the planet and see that there is something attached to its sides.