OF THE LAST TWENTY-NINE WINTERS. 37 



Here it will be seen that five years elapsed between the 

 cold winters of 1854-55 "i^d 1859-60^ but that six years 

 elapsed between the cold winters of 1864-65 and 1870-71, 

 and that eight years elapsed between the present cold 

 winter and the previous one of 1870-7 1. It is now known 

 that the sun-spot period is irregular and not so nearly an 

 interval of ten, eleven, or twelve years, as was imagined. 

 The minimum of the sun-spot period happened about two 

 years ago ; but it is still at a minimum, and very seldom 

 have spots been seen on his disk during the past year. 

 Whether these cold winters are traceable to this solar in- 

 activity or not, the present coincidence is very striking. 



In the same diagram I have presented the ratios of the 

 mean summer temperatures of the last eighteen years. 

 These ranges are included in the weekly mean tempera- 

 tures of June, July, and August, and will be seen to be 

 far less than the ranges of the winter mean temperatures. 

 This, perhaps, may be accounted for by the relative dif- 

 ference of the amount of atmospheric vapour existing in 

 the air in the two opposite seasons of the year. In the 

 winter season the ratio of atmospheric vapour reaches 87 

 per cent., whilst in the summer season it reaches only 

 about 75 per cent. But whether this is so or not, there is 

 the fact. Here it will be seen that between the hot sum- 

 mer of 1 86 1 and the still hotter one of 1868 there is an 

 interval of seven years; since then the coming summer 

 will make an interval of eleven years. In the interval of 

 seven years there was only one summer with the tempe- 

 rature slightly above the average, 1865; all the other 

 summers of this interval were mostly far below the average; 

 but in the eleven years' interval all the summers, with only 

 two exceptions, have either been above, or equal to the 

 average summer temperature. The ratios of the summer 

 and winter temperatures have not the slightest relationship 



