288 On the Derivation of the Word Theodolite. 



added; and in Stone's Mathematical Dictionary (1726) that 

 it was sometimes furnished with a telescope. 



A ruler with sights, travelling upon a graduated circle, was 

 a constituent part of various astronomical instruments im- 

 ported into Europe from the East, and was accompanied by 

 the Arabic term alhidada to express it. The word alidade or 

 alhidade (for it is spelt both ways) is completely naturalized 

 in France, and appears in the common dictionaries. It was 

 also used by the English writers of the sixteenth century, and 

 among others by Digges himself. The original theodolite 

 being nothing but a graduated circle with an alidade, some 

 connexion between the terms might be suspected by those to 

 whose notice they are brought. But so different do the words 

 appear, that I, for one, should never have been reminded of the 

 first by the second, if I had not happened to find, in a writer 

 contemporary with Digges, an intermediate formation, which 

 brings the two words nearer together. William Bourne's 

 * Treasure for Travailers ' was published in 1578 ; he does not 

 use the word theodelite, but calls the instrument the " hori- 

 zon tall or flatte sphere." He begins by spelling the word 

 alhidada thus, alydeday, but soon changes it, and keeps very 

 steadily to athelida, which is the only technical term intro- 

 duced in his description of what Digges calls theodelitus. 

 From these premises, I cannot help inferring that the theo- 

 delited circle of Digges, and the athelidated circle of Bourne, 

 which are certainly the same things, are but described by dif- 

 ferent corruptions of the Arabic word whose earliest Euro- 

 pean form is alhidada. 



In our day such a transformation might not be easy; but 

 when the works above-mentioned were written, nothing was 

 more common than to spell the same word in two different 

 ways in the course of one sentence. Bourne himself, though 

 he sometimes spells the name of Digges's work correctly, 

 Pantometria, yet in the first place in which it occurs, he makes 

 Pantometay of it, possibly a misprint for Pantometry. 



The fact seems to have been thus in this and many other 

 instances. In the sixteenth century, before the language was 

 well-settled, an author more accustomed to Latin than En- 

 glish, would try to anglicize some technical terms; and, not 

 finding his results please his own fancy, would then fall back 

 upon the Latin. Bourne has done this with both athelida 

 and pantometria ; and, were it worth while, I could show 

 abundance of similar instances in other writers. 



Nor is it against the connexion of the words that Digges 

 uses them both. Instances are not wanting in which two dif- 

 ferent spellings of the same word are used by the same writers 



