THE SENSES. 555 



which has really the same temperature as a given piece of wood will feel 

 much colder, since it conducts away the heat much more rapidly. For 

 the same reason air in motion feels very much cooler than air of the same 

 temperature at rest. 



Perhaps the most striking example of the fallaciousness of our sensa- 

 tions as a measure of temperature is afforded by fever. In a shivering 

 fit of ague the patient feels excessively cold, whereas his actual tempera- 

 ture is several degrees above the normal, while in the sweating stage 

 which succeeds it he feels very warm, whereas really his temperature has 

 fallen several degrees. In the former case the cutaneous circulation is 

 much diminished, in the latter much increased; hence the sensations of 

 cold and heat respectively. 



In some cases we are able to form a fairly accurate estimate of abso- 

 lute temperature. Thus, by plunging the elbow into a bath, a practised 

 bath-attendant can tell the temperature sometimes within 1 F. 



The temperatures which can be readily discriminated are between 

 50-115 F. (10-15 C.); very low and very high temperatures alike 

 produce a burning sensation. A temperature appears higher according 

 to the extent of cutaneous surface exposed to it. Thus, water of a tem- 

 perature which can be readily borne by the hand, is quite intolerable if 

 the whole body be immersed. So, too, water appears much hotter to 

 the hand than to a single finger. 



The delicacy of the sense of temperature coincides in the main with 

 that of touch, and appears to depend largely on the thickness of the 

 skin; hence, in the elbow, where the skin is thin, the sense of tempera- 

 ture is delicate, though that of touch is not remarkably so. Weber has 

 further ascertained the following facts: two compass points so near to- 

 gether on the skin that they produce but a single impression, at once 

 give rise to two sensations, when one is hotter than the other. More- 

 over, of two bodies of equal weight, that which is the colder feels heavier 

 than the other. 



As every sensation is attended with an idea, and leaves behind it an 

 idea in the mind which can be reproduced at will, we are enabled to com- 

 pare the idea of a past sensation with another sensation really present. 

 Thus we can compare the weight of one body with another which we had 

 previously felt, of which the idea is retained in our mind. Weber was 

 indeed able to distinguish in this manner between temperatures, experi- 

 enced one after the other, better than between temperatures to which the 

 two hands were simultaneously subjected. This power of comparing 

 present with past sensations diminishes, however, in proportion to the 

 time which has elapsed between them. After-sensations left by impres- 

 sions on nerves of common sensibility or touch are very vivid and dura- 

 ble. As long as the condition into which the stimulus has thrown the 

 organ endures, the sensation also remains, though the exciting cause 



