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XIII. On a distinct form of Transient Hemiojysia *. By Hubert Airy, M.A., M.I). 
Communicated by the Astronomer Royal. 
Received January 6, — Read February 17, 1870. 
It is certainly matter of surprise that a morbid affection of the eyesight, so striking as 
to engage the attention of Wollaston, Arago, Brewster, Herschel, and the present 
Astronomer Royal, should have received hut little notice from that profession to whose 
province it exclusively belongs. But it must be borne in mind that the votaries of 
Natural Philosophy are especially qualified by their habits of accurate observation to con- 
template attentively any strange apparition, without or within, and, I had almost said, are 
especially exposed to the risk of impairment (temporary or permanent) of the eyesight, by 
the severity of the eye-work and brain-work they undergo, and therefore possess especial 
advantages for the study of visual derangements ; whereas the physician, unless perso- 
nally subject to the malady, must depend, for his acquaintance with its phenomena, on 
the imperfect or exaggerated accounts of patients untrained to observe closely or record 
faithfully. The complaint cannot be a rare one ; each writer on the subject, in addition 
to his own personal experience, has mentioned instances of the same affection among 
his friends. In the whole body of the medical profession there must be many who are 
at once liable to the disease and able to describe it. And it is not unimportant. I have 
seen a person, terribly subject to these attacks, shudder at the very name, and turn away 
in horror from a drawing of the ugly sight, quite content to bear serious illness “ if only 
the ‘ half-blindness ’ would keep away.” 
I think it will appear from the various accounts to which I shall refer, and from the 
different instances which I shall bring forward, that there are more forms than one, of 
transient hemiopsia. 
The characters of that form to which I wish chiefly to direct attention, as described 
in the latter part of this paper, are so remarkable, that it is difficult to believe that such 
observers as Wollaston, Arago, and Brewster could have failed to notice them if 
present, or could have refrained from recording them if noticed. 
* Most writers have used the word ‘ Hemiopia ’ apparently relying on the analogy of ‘ Amblyopia ’ 
(dfipXvwTria, Hippocrates, Aphorism. III. 31). But I conceive that dfxfiXvioTria, from dpfjXvuiTros, ought in 
grammatical strictness to be used of the eye, not of the eyesight (compare <pcudpu> 7 rus, bright-eyed ; nvpionos, 
fire-eyed; yopywnos, fierce-eyed), though it seems to admit of the same laxity of meaning as our word ‘ dull- 
eyed.’ ‘Hemiopia’ would mean ‘ half-eyedness.’ The form ‘Hemiopsia’ rests on the analogy of words like 
wroili'a and vno\piu, referring purely to the eyesight. 
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