94 Britain's Heritage of Science 



science by the designers and makers of instruments deserves 

 to be emphasized. Improvements in the design of an instru- 

 ment lead not only to increased accuracy but also to the 

 saving of time and labour, which is frequently of equal 

 importance ; and in this connexion we need not necessarily 

 think of the construction of the costly instruments which the 

 astronomer now requires, nor of the elaborate appliances 

 to be found in a modern physical laboratory. The most 

 effective instrumental improvements have frequently been 

 of the simplest kind, and a handy appliance, such as the 

 slide rule, saves an amount of time which in the aggregate 

 may sum up to an astonishing figure. The slide rule was 

 introduced at a surprisingly early time. Almost immediately 

 following the introduction of logarithms, Gunter constructed 

 a rod with logarithmic divisions engraved on it, but its use 

 involved the application of a pah- of dividers. The sliding 

 arrangement which is the essential feature of the appliance 

 was first used by Oughtred (1575-1660), a mathematically 

 inclined clergyman, who incidentally introduced the X sign 

 for multiplication and the symbol : : for proportion. 



There is no department of science that depends on 

 instrumental appliances more than astronomy. The con- 

 struction of mirrors and lenses, the improvement of clocks 

 and the accurate angular division of measuring circles all 

 require skilled labour of the highest kind, while the require- 

 ments of navigation severely test the ingenuity of the 

 inventor, who has to simplify the instruments and make 

 their working independent of that firm support which may 

 be obtained on dry land, but is not available on board ship. 



As an instrument of precision the telescope was almost 

 useless until some measuring arrangement was introduced. 

 A micrometer eyepiece consisting of two metallic edges, 

 the distance between which could be altered and measured 

 by a screw, was invented by a young astronomer, William 

 Gascoigne, a friend of Jeremiah Horrocks and Crabtree, born 

 about 1612, and killed in the battle of Marston Moor. The 

 Gascoignes are first mentioned in English history when Sir 

 William Gascoigne acted as Chief Justice in the reign of 

 Henry IV., and his son, George, acquired the reputation 

 of a poet, but it is not known whether the astronomer 



