226 DISCUSSION OF THE DESICCATION QUESTION. 



of New Huven has changed at all since 1778, the change amounts only to 

 a small fraction of a degree, and cannot certainly be decided from the 

 observations. It is, however, noticeable that the difference for the summer 

 months is quite large, considering the length of the period from which the 

 result is deduced, and seems to indicate a slight moderation in the heat of 

 our summers." * 



It should be noticed here that the tendency of all thermometers is to rise, 

 as already explained ; and that if, as it appears, the instruments were not 

 carefully corrected from time to time, the results of the observations are 

 very probably higher than the truth. 



Mr. Schott has worked up the temperature observations collected by the 

 Smithsonian Institution, embracing a large amount of very poor material, 

 mostly taken by volunteer observers with little regard to scrupulous scien- 

 tific accuracy.! His results, in so far as they concern the point under dis- 

 cussion, are summed up by him in the following words : " There is nothing 

 in these curves [of secular change in the mean ainiual temperature] to 

 countenance the idea of any permanent change in the climate having taken 

 place, or being about to take place ; in the last 90 years of thermometric 

 records, the mean temperatures showing no indication whatever of a sus- 

 tained rise or fall. The same conclusion was reached in the discussion of 

 the secular change in the Rain-Fall, which appears also to have remained 

 permanent in amount as well as in annual distribution." t 



It must again be called to mind that, in spite of Mr. Schott's declaration, . 

 there may have been during the time specified a diminution of the tempera- 

 ture, to a not inconsiderable amount, counterbalanced apparently, however, 

 by the already mentioned tendency of all thermometers to rise, not uncom- 

 monly as much as one or two degrees, which rise may and often does con- 

 tinue through several years. In short, a result apparently indicating that 

 the thermometer has remained stationary is in reality more likely to be a 

 proof of a real sinking of the temperature, unless it is shown, at the same 

 time, that this source of error has been most carefully guarded against by 



* 1. c, p. 237. 



t Tables, Distribution and Variations of tlie Atmospheric Temperature in the United States, and some Adja- 

 cent Parts of America. By Charles A. Schott, 1876. Smithsonian Contributions, Vol. XXI. 



t 1. c, p. 311. The reader will notice that during the century when tliis country was being most ruthlessly 

 sti ipped of its forests, the examination of the recorded rain-fall appears, according to Mr. Schott, to have " re- 

 mained permanent in amount, as well as in annual distribution." This item of evidence may be added to what 

 has been already given on this point in a [neceding section. 



