64* Dr Gillies on a peculiar yrndijication of Vision, 
expected from their actual removal to their apparent dis~ 
tance. 
Sf That external agents exerted no influence in producing 
or removing this state of the vision, which seemed to be wholly 
dependant on causes situated in the eye itself. The circumstance 
of its never having appeared while employed in some particu- 
lar occupations, may have been purely accidental, from my never 
having been so engaged while there was a disposition in the eye 
to assume this state. 
Any further remarks I leave to those more conversant than 
myself with the science of optics, and should be happy to hear 
their opinions on the subject, and will with pleasure attend to 
the suggestion of any of your readers, should any method occur 
to them whereby I might vary and extend these observations, 
in the event of my being again affected with this modiflcation of 
vision. I am, &c. 
S. Hay Street, 1 John Gillies. 
October 1819. j 
Art. ^.—Description of a new Atmometer, invented by Adam 
Anderson, Esq, A. M. Hector of the Academy, Perth 
The Atmometer, or, as it is sometimes called, the Evaporo- 
meter for measuring the quantity of water evaporated in any 
given time, is an instrument which has not till lately been 
brought to any great degree of perfection. A circular basin, of 
uniform width from top to bottom, filled with water, is the sim- 
plest form of the instrument, and the quantity evaporated may 
be very accurately ascertained by means of a graduated glass 
tube, similar to that employed for measuring the depth of 
rain. There are several difliculties, however, attending the use 
of the instrument, which render it a very uncertain indication 
of the absolute quantity evaporated. If it be exposed freely 
to the sun and wind, the heat acquired by the vessel itself will 
rapidly promote evaporation ; and if the basin be kept nearly 
full, as it ought to be, the water will be agitated and thrown 
* The following account of this beautiful instrument is copied, by permission, 
from the MS. of the article Meteorology^ drawn up for the Edinburgh Encyclopaedia. 
