46 On ike Case of Miss Margaret MacAvoy. 



fcrred to p. 62, wherein she compares the red and orange rays 

 to gold. 



Again: with respect to fluids, it is a known law that the nearer 

 a Hquid is to the temperature at which it boils, the greater is the 

 expansion produced by the addition of a degree of caloric. In con- 

 formity with which law she ought to be more alive to the impres- 

 sions received from alcohol which boils at 176, than to water 

 whose boiling temperature is 212, and the proof is equally satis- 

 factory; for, in answer to the question, How do you know the 

 difference between water and spirits of wine, she replies " By 

 the spirits of wine feeling warmer than the water." p. 110. 



I shall conclude these remarks with one observation more re- 

 specting glass. She is asked, p. 110, " Do you feel the colours 

 equally well if two glasses are placed before the object ?" She says, 

 " If these glasses are very close to each other, I feel the colour, 

 but it appears more faint ; but if they are placed at a distance 

 from each other, I do not feel the object." This is, 1 conceive, 

 what might have beeri expected from the nature of glass, which 

 is known to be a bad conductor, though as a recipient medium 

 for the rays of light it is essential in other experiments. 



Such, sir, are the remarks I beg to offer upon this extraor- 

 dinary case : — separately considered they may be of no great 

 weight, but collectively they afford at least a curious coincidence ; 

 and the furtlier I have attempted to follow them up, the more sa- 

 tisfactory has been the result. This theory accounts for the cu- 

 rious fact stated p. 83 ; Her powers appear to be evanescent, and 

 the caloric has not at all times its occasional influence upon the 

 nerves. Accordingly, in feeling the colour possessed of the 

 smaller quantity — blue — it ceases to excite, or but feebly. The 

 colour therefore under inspection would appear to her to be im- 

 mediately changed to black. What are Dr. Renwick's words? 

 " The last colour she told was llue^ and in an instant it was 

 black, and then the power is gone !" 



If the coincidence be not purelv casual, and the conclusions 

 above mentioned not erroneous, it would be desirable to try a 

 series of prismatic experiments by the light of a full moon. For 

 the lunar spectrum being devoid of caloric, it mi2;ht be presumed 

 she would feel more diflicultv in discovering its colours than when 

 submitted to the solar rays. It might also be satisfactory to know 

 what impressions she received from the action of the solar pris- 

 matic rays extending beyond the spectrum which are purely ca- 

 lorific and colourless. I have been the more anxious to trans- 

 mit these remarks to the public through the medium of your 

 Magazine, as I trust, they may induce more scientific observers 

 to suggest experiments of a more decisive nature. I am aware 



that 



