1 J 4 Mr Harvey on the Effects of Time 



of sulphur, or is "formed of an atom of potash and one atom 

 of hydrogen combined with five atoms of sulphur. 



In concluding this note, I may remark, that M. Berzelius 

 admits, page 11G of his Memoir, that the hyposulphurous acid 

 can unite with a base in three different proportions, and that 

 it may contain the same quantity of oxygen as the base, or 

 twice or three times as much. But we must only regard 

 those compounds as definite, which can, with certainty, be ob- 

 tained in a separate state ; and as this has not been done with 

 respect to those described by Berzelius, the distinction which 

 he has drawn does not appear admissible. The last of these 

 combinations, in which the acid contains three times more oxy- 

 gen than the base, would obviously be acid, and hitherto it 

 has not been obtained. 



Art. XXIV. — On the Effects of Time in Modifying Anoma- 

 lous Cases of Vision with regard to Colours. By George 

 Harvey, F. R. S. Lond. and Edin., F. G. S. &c. In a 

 Letter to the Editor. 



My Dear Sir, 



In the Seventh Number of your valuable Journal, you have 

 given an interesting abstract of several anomalous cases of 

 vision, with respect to colours ; and it has occurred to me, 

 from reflecting on the case which I laid before the Royal So- 

 ciety of Edinburgh, and which is shortly to be published in 

 the Transactions of that learned Body, that time may possi- 

 bly produce some modifications in those peculiar conditions of 

 the retina, by which some individuals are prevented from at- 

 taining correct perceptions of colour. 



With respect to that general decay of vision, which time 

 commonly produces in eyes, in every respect perfectly or- 

 ganized, it may be remarked, that those perceptions of colour, 

 which are active and perfect in youth, are commonly preserv- 

 ed through life, with no other change than that general dimi- 

 nution of their vividness and intensity which the natural de- 

 cay of the energies of the retina may be supposed to produce, 



