METHODS OF INVESTIGATION. 25 



liim number 190, a,ud there are briefer references to very many more. 

 Loflfelliolz-Colberg's list begins with Fernando Columbus, the son of 

 Christopher Columbus, who attributes the heavy rainfall on Jamaica 

 to its wealth of forests, and the decrease of rain on the Azores and 

 Canaries to the removal of their forests. In the sixteenth and seven- 

 teenth centuries the subject was already attracting the attention of 

 the French Government, and in fact governmental interest in the sub- 

 ject goes back to the time of the immediate successors of Charlemagne. 

 It is interesting to read over the abstracts of opinions which are recorded 

 in Lott'elholz-Colberg's smallbook. Every variety of opinion can be found 

 there, from those which attribute to the forest about everything which is 

 desirable in climate and even endow it with a powerful influence on mor- 

 als, to those who believe it is entirely without influence ; and from those 

 who think that its influence does not extend bej^ond its own margin, 

 to those who would attribute the deterioration of the climate of the 

 Old World to the removal of the forests of the New. The reasons for 

 this extraordinary variation in opinion are to be found in the method 

 employed for solving the problems of forest meteorology. Leaving out 

 of account the solutions which were purely sentimental or purely tour- 

 istic, the conclusions were generally founded on what may be called 

 the historical method. This consists in finding a country which has 

 been once wooded, but from which the forests have been removed, 

 or one which was once open, but later became wooded. The clinuite at 

 the beginning and end of the time involved is then ascertained or 

 assumed, and the changes in the climate are attributed to the change 

 in the forest cover. The uncertainties of this method are so great as 

 to make it generally useless. It is seldom possible to be sure of the 

 early forest condition of the country in question. For this purpose 

 reliance must generally be placed on incidental references by the earl- 

 ier writers, and these are usually ambiguous and uncertain. Even 

 where the change in forest conditions can be proved bejond the possi- 

 bility of doubt, the character of the early climate can not be ascer- 

 tained with a sufficient degree of accuracy. If the period in question 

 preceded the introduction of meteorological instruments, then the char- 

 acter of the cliuuite must be judged by the nature of the crops raised or 

 from facts of a similar nature given by earlier writers. If observa- 

 tions were taken they were generally rude and by means of imperfect 

 instruments: their errors would probably approach in magnitude the 

 quantity of forest influence which is to be determined. Besides, the 

 fixing of the data of climate with our modern exact instruments and 

 better methods requires observations for a long series of years. The 

 variations of the elements of climate (the temperature, humidity, rain- 

 fall, winds, and cloudiness) are great from day to day and from year 

 to year, and it takes numerous observations, scattered through many 

 years and taken on a uniform system, to give fixed values for the cli- 

 mate. The rainfall tor two successive years on the same spot might 



