MODE OF PLANNING AN EXPERIMENT. 309 



of such materials as are most ready at hand. The un- 

 essential parts of such a model may generally be of the 

 roughest kind, but the essential conditions, as far as we 

 know or can guess them, should be fulfilled as perfectly 

 as possible. For example, if a feeble rotatory effect is 

 sought for, the friction of the moving parts should be 

 reduced to a minimum, and the motive power exalted to 

 the highest degree. Circumstances which, we feel assured, 

 do not affect the results, such as crudeness of some parts 

 of the apparatus, and in some cases even impurity of the 

 materials, may be entirely disregarded ; but this point can 

 only be determined by actual knowledge, and should not 

 be acted upon unless we are quite certain. Eminent 

 investigators have usually constructed the apparatus used 

 in their first experiments on a subject in a rough sort of 

 way ; the model of the first safety-lamp made by Sir 

 Humphry Davy was formed by wrapping a piece of wire- 

 gauze round his thumb, and is now in the possession of the 

 Eoyal Society. Undue fondness for beautiful apparatus 

 is, in the adult student, rather a sign of an amateur than 

 of an original mind. When an investigation is completed, 

 an apparatus, perfect in appearance and durability as well 

 as in action, may then with propriety be constructed. 



As new phenomena, when first discovered, are often 

 very minute, the proportions of the different parts and 

 conditions of the experiments should be very carefully 

 considered at the outset, or as soon as possible ; for want 

 of this, early experiments often fail, which, if properly 

 arranged, would have succeeded. Where the effects are 

 extremely minute, they are magnified or multiplied by 

 means of various contrivances, which differ in almost 

 every different case, and these contrivances are described 

 in books relating to the various sciences. The pendulum 

 is a well-known means of magnifying, by multiplication, 



