ESSAYS 659 



The second consideration is that when this hypothesis of the existence 

 of real external substance has been sufficiently verified it does not differ 

 in any respect from the rest of our knowledge. As in the case of our other 

 concrete hypotheses, repeated tests are necessary before the verification 

 can be deemed adequate. But these are so superabundant, even in early 

 life, that if certainty be denoted by unity, the difference between this and 

 the validity of the hypothesis of reality might be denoted by that between 

 unity and the recurring decimal 0-9 ; a difference which is less than any 

 assignable quantity. Reality, therefore, cannot be excluded from the 

 scope of our knowledge unless everything else, beyond bare sensation, be 

 also excluded. 



Very concisely, then, the core of the theory now propounded is that the 

 mental processes concerned in the production of knowledge are of two kinds, 

 the direct reactions of the organism to stimulus, and the hypotheses by 

 which the remembrances of these reactions are associated in series ; that 

 the immediate object in view is the making of forecasts for the future on 

 the basis of the hypothesis that the series will recur ; and that the success 

 of forecasts is the sole test of the validity of hypotheses. Those of the 

 present theory are framed for the purpose of forecasting how fresh know- 

 ledge will be attained, and must be subject to verification by farther experi- 

 ence of its progress. 



It is the ultimate object of knowledge to be the guide of action. 



Unless a theory can in some way conduce to that object I attach little 

 value to it ; my hope is that this one will serve as a guide in future 

 methods of education. 



THE PURIFICATION OP MOORLAND WATER SUPPLIES 



(Ernest G. Blake, M.R.S.I., A.B.I.C.C.) 



A considerable difference frequently exists in the composition of water 

 which is obtained in certain districts, although they may not necessarily be 

 widely separated, the variation arising from purely local causes. The charac- 

 ter of the water naturally exerts an appreciable influence on the health and 

 well-being of those who use it for drinking and culinary purposes, and the 

 origin of various more or less serious disorders is commonly ascribed to this 

 source. Hard water — i.e., water which contains an excess of lime — is 

 popularly supposed to be the predisposing cause of goitre or Derbyshire neck, 

 gravel, etc., from the fact that the system becomes clogged with the lime after 

 continuous use. It is also responsible for various troubles apart from the 

 human frame, and is the direct cause of the " furring " which occurs in boilers 

 and cooking utensils, when the lime collects on the sides and bottom of the 

 apparatus in the form of a hard, insoluble incrustation, commonly known as 

 scale. Water which contains less than six grains of lime to the gallon is 

 considered to be soft, and is less troublesome in this respect. In this condition 

 it is decidedly preferable for domestic purposes. 



The supply which is collected on a peaty gathering-ground may, on the 

 contrary, act in a reverse direction, and may be of such a nature as to destroy 

 almost any metal with which it comes into contact, its corrosiveness varying 

 with the class of soil from which it is drawn. This destructive tendency is 

 caused by the excessive softness of the water, combined with the presence of 

 humic acid, which is gathered from the vegetable constituents of the soil as it 

 percolates down through the ground. Peaty water is usually of a clear brown 

 colour and is very similar in appearance to weak tea, although it does not 

 thereby necessarily produce dangerous consequences when consumed ; but 

 when it is strongly acidic the pipes and metallic fittings deteriorate so rapidly 

 a9 to constitute a very serious problem, as to how these effects are to be 

 neutralised without going to undue expense. The trouble is much more 



