1C6 Portable Equatoreals. 



PORTABLE EQUATOREALS. 



EY WILLIAM C. BURDER, F.R.A.S. 



It is perhaps more important in regard to astronomical in- 

 struments than to most others, that there should be in the 

 minds of those who use them distinct ideas of the objects in 

 view in their construction, and their capabilities and limits as 

 to usefulness. 



Without such ideas, amateurs are very apt to make a false 

 start, and to find themselves, consequently, obliged to return to 

 their starting point, disappointed, both with their own work, 

 and with the instruments which they have been attempting to 

 use. Perhaps no instrument stands in need of this prefatory 

 remark more than the Equatoreal, a name which probably 

 conveys to the mind of the beginner an impression, in most 

 cases, of a very different instrument from the one which his 

 subsequent experience discovers it to be. To the professional 

 astronomer who possesses a good steady working equatoreal, 

 and who has no leisure for astronomical recreation, as such, it 

 is easy to imagine that the term " portable/' applied to equa- 

 toreals is by no means suggestive of pleasing associations. 

 The very great difficulty experienced in constructing the larger 

 sort of instruments, so as to combine great steadiness with a 

 perfectly easy motion — qualities absolutely essential to their 

 good performance — and the variety of causes which have a 

 tendency to introduce sources of error in the working of the 

 equatoreal, are reasons why the thoughts of the professional 

 astronomer in reference to these instruments are likely to be 

 very different from those of the amateur whose aim is astro- 

 nomical amusement and instruction, rather than the advance- 

 ment of the science, even in a feeble manner. The possessor 

 of the portable equatoreal must consider himself happy if he 

 finds his instrument a means of using an ordinary telescope to 

 much greater advantage than would be possible without its aid. 

 That he may do this there is not the slightest doubt. Indeed 

 it is not too much to say that a simple equatoreal mounting for 

 an ordinary pockel telescope multiplies its usefulness fourfold, 

 or perhaps much more. We may take it for granted that 

 the readers of the many interesting astronomical papers which 

 have appeared in the Intellectual Obskkyek, do not most 

 of them require that many remarks should be made on the 

 general principles of equatoreals ; still, as there are always 

 new readers to every article, the former class will, it is hoped, 

 forgive the writer if be goes somewhat over old ground in a 

 lew preliminary remarks, in order to make the description 

 more complete to the latter class. 



