24 THE POSSIBILITIES OF THE TELESCOPE. 



the diurnal motion of the earth. To give the proper motion 

 to the telescope the most accurately constructed driving clock- 

 work is necessary. For planetary detail, however, I much 

 question if photography will ever render much service. There 

 is no getting over the blurring caused by atmospheric dis- 

 turbances, superadded to instrumental imperfection. The 

 photo of moon from the great Melbourne telescope is 

 generally accounted one of the most successful ever produced. 

 But in this, minute details that are distinctly visible in either 

 of my comparatively small telescopes are totally absent. 



A few remarks on the necessity of caution in rightly inter- 

 preting telescopic appearances may fittingly conclude this 

 paper. A novice on taking his first peep at the planets, we 

 will suppose, will probably feel quite disappointed that the 

 object he sees exhibits very little of the detail or appearance 

 of that same object as depicted and described by experienced 

 observers, and after long and diligent observation. The eye 

 requires considerable training for this kind of seeing. More- 

 over, considerable judgment is necessary in rightly interpret- 

 ing what we see. 



ERRATA (in Plate). 

 Omit the words " Page A," etc. 

 u In Fig. 2 b add a dotted line (A) from prism, above C." 



