SCIENTIFIC PICTURES OF JOSEPH WRIGHT 433 



Taking the pictures in the order in which they were painted, 

 we may regard " The Orrery," " The Air-Pump," and " The 

 Alchymist " as typical of the state of development of the 

 sciences of astronomy, physics, and chemistry respectively, 

 in the latter half of the eighteenth century. 



To " The Orrery," which was exhibited in the year 1766, 

 the artist gave the title " a philosopher gives that lecture on 

 the Orrery, in which a lamp is put in the place of the sun." 

 By the term philosopher we are to understand a natural philoso- 

 pher, i.e. one whose studies had embraced, besides a sufficiency 

 of mathematics, the subject of mechanics, including statics 

 and dynamics, astronomy and other branches of physics so 

 far as they were then developed. With the progress cf speciali- 

 sation the term natural philosophy has fallen into disuse. 



In Wright's day the science of astronomy was already 

 firmly established on thoroughly sound foundations. Observa- 

 tional astronomy is, of course, one of the oldest of sciences, and 

 eastern shepherds in distant ages, mariners in all ages, and 

 possibly even men of the Stone Age, were far more familiar 

 with the magnificent spectacles which the heavens present to 

 our gaze than is the average town-bred product of a modern 

 education. 



Copernicus, in the first half of the sixteenth century, was 

 able to show, as the result of many years of careful observation 

 and calculation, that the earth is not the immovable centre 

 of the universe around which the heavens revolve, as was 

 commonly beHeved during the Middle Ages, but that, hke the 

 other planets, it revolves round the sun. Kepler early in 

 the seventeenth century, by studying the valuable observations 

 of Tycho Brahe, established laws which accurately describe 

 the motions of the planets in elliptical orbits with the sun in 

 one of the foci. Galileo about the same time constructed a 

 telescope and applied it to the study of the heavens. He was 

 richly rewarded by the discovery in succession of the difference 

 in the appearance of a planet and a star, the moons of Jupiter, 

 the phases of Venus, the rotation of the sun, and the mountains 

 and valleys of the moon. We owe to the genius of Newton, 

 in the latter half of the seventeenth century, the laws of motion 

 and the law of gravitation, which explain why the planets move 

 in the manner described by Kepler and thus place the science 

 of physical astronomy on a sure basis. 



The picture takes its title from the instrument portrayed. 

 It is a contrivance for representing the positions and motions 

 of the heavenly bodies and, generally speaking, for illustrating 

 the facts and principles of astronomy. It has a very wide 

 range of useful application, and by its means the leading truths 

 of the science may be demonstrated to those who are unable 



