414 PROFESSOR C. PIAZZI SMYTH ON THE v 



finally that, as to the small stars picked up by the Elchies instrument, in a trial 

 of that kind, round about 312 Pegasi, No. 27 of our list, he, the objector, had 

 since quite rapidly identified them all with his 8*5-inch glass. 



The mere measure, however, of the area in inches does not satisfy every one 

 thus easily, as to each of the many varied star-showing properties or failings of a 

 large object-glass: and the identification quoted above, leaves perfectly untouched 

 two most important data in the problem, viz., Ist, The different quality of the two 

 observers' eyes in the two cases, and they may be most extraordinarily different 

 in vigour, sharpness, sensibility or other important optical bearings ; and, 2d, The 

 fact that the one observer discovered and micrometrically measured the objects, 

 while the other merely identified them from these measures when printed, and 

 placed in his hand. Much is also due on every occasional trial, to the light-trans- 

 mitting and defining power of the atmosphere at the place ; whence, a long 

 series of observations, giving a general mean, should be more convincing than 

 some one special and particular attempt. 



Now in the " Cycle," there is a grand mass of evidence of what a good eye was 

 enabled to do, on the average of many 3^ears, in an English atmosphere, with a 

 5-9-inch object-glass ; that book, therefore, I make my honoured point of reference 

 in the three following cases : — 



First, Avith a 3-6-inch object-glass I have worked for many nights at the 

 ■' Cycle" objects in the clear atmosphere of Mount Guajara, but could not, 

 with all my pains, and with all the advantages of that pure and well-defining 

 atmosphere, see all, or by any means all,. that the Cycledescribed. 



Second, with a 7'25-inch object-glass, I have similarly worked away at the 

 same subjects, and saw without difficulty, anomalies excepted, every feature 

 described in the Cycle ; but I hardly saw anything more. 



Third, with the Elchies 11 -inch, in the bad Elchies atmosphere, I similarly 

 saAv, not only without difficulty, but with ease, whatever, even most minute, was 

 described in the Cycle ; and beyond that saw and measured, in not a few cases, (I 

 do not say that they were well defined or adapted for making good measures,) 

 other small stars that had neither been described in the respected pages of the 

 Cycle, nor seen with the 7'25-inch object-glass in the purer climate of Alta Vista. 



Here therefore is proved, and in an intensely practical manner, the advantage 

 of size generally; also, that together with its superior dimensions, the great 

 Elchies Telescope really has increased optical power proportioned worthily 

 thereto, for distinguishing small isolated stars, whether their existence has been 

 already recorded or not ; while the pleasure and satisfaction its use on that 

 account alone imparted to me, is what only an ardent, and previously often foiled, 

 observer can fully appreciate. What would such an instrument not have done 

 in absolute stellar discovery, if the sharper eye of him with the 8-5-inch object- 

 glass, had been employed in utilizing its admirable manifestations ! 



