"When something embarrasses you do not abuse the help of your colleagues; with assistance the difficulty is only evaded; with patience and reflection IT IS OVERTHROWN. Moreover, one knows thoroughly only what one learns oneself; and I advise you earnestly, as far as possible, to have recourse to no aid other than reflection, above all for the sciences. A book of science is an enigma to be deciphered; if some one gives you the key of the enigma nothing appears more simple and more natural than the explanation, but if a second enigma presents itself you will be as unskilful as you were with the first... "It is probable that you will get the chance of a few lessons; do not by preference accept the easier and more lucrative, but rather the more difficult, even when the subject is one of which as yet you know nothing. The self-esteem which will not allow one's true character to be seen is a powerful aid to the will. Do not forget the method of Jules Janin, running from house to house in Paris for a few wretched lessons in Latin: 'Unable to get anything out of my stupid pupils, with the besotted son of the marquis I was simultaneously pupil and professor: I explained the ancient authors to myself, and so, in a few months, I went through an excellent course of rhetoric...' "Above all you must not be discouraged; time is nothing provided the will is always alert, always active, and never distracted; 'strength will come as you travel.' "Try only for a few days this method of working, in which the whole energy, concentrated on one point, explodes like a mine and shatters obstacles; try for a few days the force of patience, strength, and perseverance; and you will see that nothing is impossible!" (2/4.) These serious reflections show very clearly that his mind was already as mature, as earnest, and as concentrated as it was ever to be. Not only did he join example to precept; he looked about him and began to observe nature in her own house. The doings of the Mason-bee, which he encountered for the first time, aroused his interest to such a pitch that, being no longer able to constrain his curiosity, he bought--at the cost of what privations!--Blanchard's "Natural History of the Articulata," then a classic work, which he was to re-read a hundred times, and which he still retains, giving it the first place in his modest library, in memory of his early joys and emotions.