Ill 



REMARKS ON SURFACE TEMPERATURE AND ON 

 THE EFFECT OF SHELTER. 



By C. BAEHAM, M.D., Cantab. 



At our last Spring Meeting I ventured to draw attention to the very 

 considerable difference between the lowest temperature of the night indicated 

 by the self-registering thermometer, placed, as it usually is, on a stand or 

 under a shed, and that shown by a similar instrument exposed on the grass, 

 and radiating freely into space. This difference is in itself an illustration of 

 the influence of shelter ; and the importance of its bearings on plants and 

 animals has made it worth some special inquiry through the agency of this 

 Institution. I am particularly indebted to Mr. Moyle of Helston and Capt, 

 Liddell of Bodmin, who have made continuous observations on surface tem- 

 perature in those places through a long series of years, for placing their 

 results at my disposal; and to Mr. R. W. Fox, F.E. S., in the neighbourhood 

 of Falmouth, for purposely instituting a like record for our service ; whilst 

 Mr. Whitley has lent most ready and valuable aid to the investigation. 



It may be safely affirmed that the common estimate of the greatest cold 

 of night is derived from the record of the thermometer on the stand or 

 in the shed. • This is what passes current as the minimum, and that not 

 only among the public, but also generally with those who pay a good deal of 

 attention to meteorology. Yet when the sky is clear, the temperature of the 

 grass, that to which vegetables and man and animals out of doors are 

 exposed, will be from five to ten degrees lower, sometimes more ; and it is 

 just these additional degrees of cold, when the ordinary sheltered thermometer 

 indicates pretty sharp frost, that destroy tender plants, and often nip, more or 

 less seriously, the delicate and the very old and very young. I remember 

 having been struck by an account about fifty years ago of the guard of the 

 Bath Mail having been frozen to death one night in June. It was a bitter 

 spring all through— and, no doubt, the poor fellow, not dressed for winter, 

 was benumbed into his death sleep by 15 or 20 degrees of frost ; whilst people 

 judging from the ordinary register, which indicated a cold of moderate 

 severity, wondered that a strong man should thus perish. 



It is needless to dwell on the recognized cause of this loss of heat, its 

 radiation from the earth's surface ; or on the established fact that all opaque 

 bodies, distant as well as near, which intercept its passage into space, send 

 that heat back again, and thus more or less abate the cooling process. This 

 fact must, however, be kept in mind as of practical bearing on differences of 

 surface temperature as observed in distant places, and even in different 

 parts of this county, as they vary in cloudiness or in moisture of atmosphere. 



Turning then to the materials at our command for ascertaining the 

 surface temperature in Cornwall — Helston and Bodmin have furnished as 

 I have said, records of surface observations by self-registering thermometers 

 for many successive years. Mr. Moyle has placed his instrument on the top 

 of a box edging in his garden ; Capt. Liddell's has been laid on the grass. 



