256 
zizgag outline described, very faint and shadowy, without any 
other disturbance of the system ; it lasted about ten minutes. 
Dr MicHArEL Foster asked whether Dr Latham had had 
the opportunity of seeing any patient during the attack itself, 
so as to see how far the blood-vessels and the pupils were 
affected. 
Dr LATHAM said that he had recently seen two cases during 
the headache, the pupil was then contracted; but he had not 
lately seen a case during the time of the peculiar affection of 
the vision. 
Dr M. Foster said that though Dr Latham had given a 
general explanation, he had not brought the explanation suf- 
ficiently near to the particular case; that the special descrip- 
tion of teichopsia could only be A a when we knew some- 
thing more about a very complex matter, the vaso-motor centres 
of the brain; he also thought that the phenomena described 
might possibly be produced by some affection of the circulation 
in the retina. 
Dr LaTHAM said he was quite aware that some difficulties 
yet remained in his explanation—he had indeed thought that 
the minor cases of the disorder might be produced by some 
affection of the ophthalmic artery. 
The PRESIDENT said that he was not inclined to attribute 
it to the ophthalmic artery, but rather to the brain, whether 
vascular or not could not yet be said. 
(2) A machine for tracing Curves described by points 
of a vibrating String; namely, curves of the 
forms 
2ar i Aa ‘ 
w=acos(t+a), y=bsin (7 t+8), 
1 
