Without reason no effect is produced in nature; understand the reason and you will not need experience.
Cause discovered by Effect
68.
Before I proceed further I will make some experiments, because it is my intention to cite the experiment first and then to demonstrate by reasoning how such an experiment must necessarily take effect in such a manner. And this is the true rule by which investigations of natural phenomena must proceed; and although nature herself begins from the reason and ends in the result, we must pursue the contrary course and begin, as I said above, from experience and by it seek out the reason.
Repetition of Experiment
69.
Before deducing a general rule from this case repeat the experiment two or three times and see if the same results are produced.
Example of preceding Rule
70.