248 Prof. Heunessy on the Distribution 



could not be included ia any of these groups, as their tempera- 

 tures were respectively 49°-6 and 47°*3. 



Before I had made these combinations. Dr. Lloyd had re- 

 marked the singular difference between the temperature of the 

 inland stations and those on the coast. In the small map which 

 accompanies his memoir, the isothermal lines are deduced from 

 the coast observations alone ; and the author thus seems to indi- 

 cate that these lines are intended to show the isothermals of the 

 air over the sea surrounding Ireland, but not the distribution of 

 temperature within the island itself. From the comparatively 

 regular forms of such lines on the surface of the ocean. Dr. Lloyd 

 assumed that over a small space they might be regarded as ap- 

 proximately straight; and he was thus enabled to apply the 

 method of least squares for the precise determination of their 

 positions. 



As I could not assume any definite form for the interior 

 isothermals, I could not use the method of least squares, and 

 have had to lay them down by the ordinary method of tracing 

 curve lines, each of which runs through a group of stations of 

 equal temperature. 



On looking at the map, it is apparent that, having first traced 

 the isothermal of 52° which runs along the south-west coast near 

 Cahircivcen and Castletownsend, the isothermal of the next 

 lowest temperature must fall completely inside it, for two differ- 

 ent isothermal lines cannot intersect. But the line of 51° runs 

 from Mayo to Watcrford, and is much longer than the line of 

 52°. The isothermal of 50° must in like manner be included 

 within this, and it terminates on the north-east and north-west 

 coast res])ectively. Thus we have three open isothermals, until 

 we come to that of 49°, which runs along the north coast near 

 Portrush and Buncrana. But as this must be included within 

 the preceding, it would, if produced at each exti-emity, form a 

 re-entrant curve. The isothermal of 48° passes within that of 

 49°, and through places not far from the inland stations, Armagh, 

 Athy, and Markree*. The station of least temperature, Portar- 

 lington, should be situated within this line; and it actually does 

 lie between Markree and Athy, although much nearer to the 

 latter. Any other places possessing the same mean temperature 

 as Portarlington must be situated within the isothermal of 48°; 

 and an isothermal ])assing through Portarlington would be a 

 closed curve. Donaghadee, on the north-east coast, lies, as should 

 be expected, outside the isothermal of 49°, and inside the pro- 

 longation of the isothermal of 50°. 



AH these results completely harmonize with the views I have 

 i)ut forward ; and I feel perfectly assured that further observa- 



* See the Table of mean annual temperature for Ireland at the end. 



