The “Popular Reflector,” with 5-1/4 inch speculum of 5, 5-1/2, to 6 feet focus, will be found very suitable, and if its illuminating power is not greater than a 4-1/2 inch refractor, its defining and dividing powers are superior. By choosing the above focal lengths, according to circumstances, the observer can reach the eye-tube, while standing erect for objects in the zenith, and it is a great mistake to suppose that the shorter the tube the more handy it becomes. These foci will not require a “Barlow” lens to flatten the field. The “Barlow” is very useful for short foci when the aperture is considerable, as it improves the imperfect correction for spherical error, but this is much better corrected in the mirror itself than by a “Barlow” lens, which cannot be used without more than one disadvantage. There must, by its insertion, be some loss of light, which can ill be spared with small instruments, and when used to obtain magnifying power there is some disturbance of colour, and this subtracts from the beauty and purity of the definition of a reflector. There is _nothing_ equal to a good eye-piece to obtain _power_, and _flatness_ of field by the _curve_ of the speculum.
With the “Popular Reflector” and an outlay of a few shillings on some popular books, such as the excellent work “Celestial Objects,” by the Rev. T. W. Webb, and some first-class publications by Mr. R. A. Proctor, especially his smaller star atlas, &c., the amateur can compare the work he is then capable of doing with a large and expensive refractor which might be beyond his reach.
When the inexperienced amateur purchases an equatorial with circles, he should not be without the third edition of “Chamber’s Handbook of Descriptive Astronomy,” which, besides being an excellent book in other respects, is a really practical guide to the use and application of the Equatorial, and is indispensable to the beginner. He will there find the fullest details of the adjustments to any degree of exactness. Besides many other matters he will be instructed in the use and application of apparatus to the perfect Equatorial, including all kinds of eye-pieces, micrometers, &c., &c., as well as other optical instruments and accessories.