206 Mr. W. F. "Barrett on Sources of Error in 



But habits created by magnitude may cause mistakes of vi- 

 sible distance involving also the image in the axis. 



Thus, for example, if the mind has been accustomed to ap- 

 preciate the images of mountains of moderate magnitudes, thereby 

 tendencies will be impressed upon it to appreciate moderate di- 

 mensions with images of this class. Hence, when the image 

 of a mountain of extraordinary magnitude is presented (in an 

 ordinary state of the atmosphere), consciousness will be influ- 

 enced to appreciate the dimensions as less than they really are, 

 and, in order to this, the distance from the base of vision as a 

 duly less one. And the effect on any concomitant images, as of 

 trees or animals, would be a like seeming diminution of their 

 visible magnitudes. For it is plain that if consciousness makes 

 a mistake of distance, then, in obedience to the law of habit, it 

 will assign that size which the image would really have at that 

 distance, or that effect of lateral distance, or resulting expansion, 

 which the divergence of the lines of direction would give at that 

 distance. 



Dr. Abercrombie relates the following instance as having oc- 

 curred in his own experience. "I remember," he says, ie once 

 having occasion to pass along Ludgate Hill when the great 

 door of St. Paul's was open and several persons were standing 

 in it. They appeared to be very little children ; but, on coining 

 up to them, were found to be full-grown persons." 



The theory which I have thus advanced, taken in connexion 

 with the mistaking practice of consciousness, will, I believe, 

 furnish a satisfactory explanation of all the phenomena of vision, 

 some of the more interesting of which phenomena, as well as 

 the subject of monocular vision, I propose in a future paper to 

 consider. 



Hastings-upon-IIudson, New York. 



XXVII. On Sources of Error in Determinations of the Absorption 

 of Heat by Liquids. By W. Fletcher Barrett, Lecturer on 

 Physical Science at the International College, §•<?.* 



DURING the autumn of 1865, whilst engaged in determi- 

 ning for Professor Tyndall the absorption of heat by various 

 liquids, I observed that under certain conditions the more dia- 

 thermic liquids exhibited a remarkable and anomalous deport- 

 ment towards radiant heat. This observation led me to make a 

 subsequent investigation, the results of which are given in the 

 following paper. 



* Communicated by the Author, having been read at the British Asso- 

 ciation, August, 186S. 



