The Practical Astronomer Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy

The following remarks, chiefly in regard to the manner of using telescopes, may perhaps be useful to young observers, who are not much accustomed to the mode of managing these i...

_The Newtonian Reflector._--This instrument is somewhat different both in its form and in its mode of operation from that of Gregory. It is represented in fig. 63, where BAEF is...

There are two kinds of telescopes, corresponding to two modes of vision, namely, those which perform their office by _refraction_ through lenses, and those which magnify distant...

An orrery is a machine for representing the order, the motions, the phases, and other phenomena of the planets. Although orreries and planetariums are not so much in use as they...

The equatorial instrument is intended to answer a number of useful purposes in Practical Astronomy, independently of any particular observatory. Besides answering the general pu...

We have hitherto considered light chiefly as a simple homogeneous substance, as if all its rays were white, and as if they were all refracted in the same manner by the different...

The _reflection_ of the rays of light is that property by which--after approaching the surfaces of bodies, they are thrown back, or repelled. It is in consequence of this proper...

It is not my intention to discuss the subject of light in minute detail--a subject which is of considerable extent, and which would require a separate treatise to illustrate it...

Light, when proceeding from a luminous body--without being reflected from any opake substance or inflected by passing near one--is invariably found to proceed in straight lines...

Before proceeding to a particular description of the different kinds of telescopes, I shall first give a brief description of the Camera Obscura, as the phenomena exhibited by t...

It is to the refraction of light that we are indebted for the use of lenses or artificial glasses to aid the powers of vision. It lays the foundation of telescopes, microscopes,...

The telescope is an optical instrument for viewing objects at a distance. Its name is compounded of two Greek words,--τηλε, which signifies, _at a distance_, or _far off_, and σ...

I originally intended to enter into particular details on this subject, for the purpose of gratifying those mechanics and others who wish to amuse themselves by constructing tel...

A micrometer is an instrument attached to a telescope, in order to measure small spaces in the heavens, such as the spaces between two stars, and the diameters of the sun, moon...

In order to make observations, with convenience and effect, on the heavenly bodies, it is expedient that an _observatory_, or place for making the requisite observations, be ere...

In order to understand the principle on which telescopes represent distant objects as magnified, it may be expedient to explain what is meant by the angle of vision, and the app...

Light is that invisible etherial matter which renders objects perceptible by the visual organs. It appears to be distributed throughout the immensity of the universe, and is ess...

Before the achromatic telescope was invented, there were two glaring imperfections in refracting telescopes, which the astronomers of the 17th century were anxious to correct. T...

Composition of the speculum, and the process of casting it--Mode of grinding and polishing it--Manner in which it is filled up--Expenses incurred in its construction--Results of...

circumstance, in his description of an ‘Eye-piece wire micrometer,’ and complains of Mr. Ezekiel Walker, having in the ‘Philosophical Magazine’ for August, 1811, described such...

Description of its nature and construction--How its magnifying power is determined. Table of the linear aperture, magnifying powers, &c., of astronomical telescopes from 1 to 12...

1. Adjustments requisite to be attended to in the use of telescopes--2. State of the atmosphere most proper for observing terrestrial and celestial objects--Average number of ho...

Construction of this telescope, and the manner of using it--Illustrated by figures--Its properties and advantages--Tube not necessary in reflecting telescopes--How a large refle...

Colours, the beauty of nature--Opinions which were formerly entertained respecting their cause--Sir I. Newton’s experiments with the Prism--Colours and phenomena produced by the...

Nature of reflection--Plane, convex, and concave speculums--Angle of reflection--Reflection of objects from plane mirrors, illustrated by figures--_Reflection by Convex and Conc...

History of equatorials--Description of one of the simplest construction of these instruments--To adjust the equatorial for observation--To adjust the line of sight--Description...

Extraordinary appearance of the coast of France from Hastings--Appearance of a ship seen by Captain Colby, beyond the coast of Caithness--Scoresby’s view of his father’s ship wh...

Interesting nature of this study--Different hypotheses which have been formed respecting the nature of light--It radiates in straight lines--Moves with amazing velocity--Flows i...

Refraction the foundation of optical instruments--Various forms of lenses--_Parallel_, _converging_, and _diverging_ rays--Illustrated by diagrams--_Concave_ lenses, their effec...

Appearance of objects in a camera obscura--The dark chamber--This instrument serves to explain the nature of a refracting telescope--Particulars to be attended to, in exhibiting...

The telescope a noble instrument--Effects it produces--Whether known to the ancients--Friar Bacon’s ideas respecting telescopes--First constructed in Holland--The invention clai...

1. Directions for grinding lenses for eye-glasses, microscopes, &c.--2. Method of casting and grinding the specula of reflecting telescopes--Compositions for speculum metal--To...

Leading features of a spot adapted for celestial observations--Public and private observatories--Greenwich observatory--Instruments with which an observatory should be furnished...