63 
the attempt at measuring and eliminating these errors is 
found to be, — these are unquestionably the highest charac- 
teristics of the practical astronomer; and experience has 
shown that these will more than compensate for the dimmed 
eye, the unsteady hand, and the impaired susceptibilities of 
advancing years. The whole spirit of modern practical as- 
tronomy tends in this direction. Never otherwise could 
that great dictum of the immortal Struve have passed into 
an astronomical theorem : “ Whatever may be seen may be 
measured.” It is by this principle that the modern forms 
and appliances of the choicest astronomical instruments are 
regulated, and the modern methods of observation pre- 
scribed. No longer are azimuthal errors supposed to be 
eliminated by adjustment upon a meridian mark, or collima- 
tion-errors removed by analogous processes, or clock-rates 
assumed as constant through protracted intervals of time, 
nor the graduations of any instruments implicitly relied on 
for delicate determinations, nor positions based upon the 
most massive structures assumed to remain constant. The 
chief effort of the skilful observer of to-day is directed rather 
to the elimination and the measurement than to the avoid- 
ance of error; for human sense is but fallible, while human 
intellect and art are at least a reflex, if not a spark, from 
the divine altar. 
Yet despite all this, it would be folly to attempt to por- 
tray the indescribable advantage to an observer which is 
afforded by delicacy of the senses. Training will do much’ 
- but the culture of delicate perceptions must accomplish more 
than the training of average ones. And it was Gilliss’s pe- 
culiar privilege to be endowed with a wondrous acuteness 
of the perceptive powers of eye and ear, as manifested in his 
astronomical observations. No one at all conversant with — 
_ observations can examine the printed record, however casu- 
