whose utility is very remarkable:  but without any wish to depreciate it, I
am confident that there is no one, even among those whose profession it
is, who does not admit that all at present known in it is almost nothing
in comparison of what remains to be discovered; and that we could free
ourselves from an infinity of maladies of body as well as of mind, and
perhaps also even from the debility of age, if we had sufficiently ample
knowledge of their causes, and of all the remedies provided for us by
nature.  But since I designed to employ my whole life in the search after
so necessary a science, and since I had fallen in with a path which seems
to me such, that if any one follow it he must inevitably reach the end
desired, unless he be hindered either by the shortness of life or the want
of experiments, I judged that there could be no more effectual provision
against these two impediments than if I were faithfully to communicate to
the public all the little I might myself have found, and incite men of
superior genius to strive to proceed farther, by contributing, each
according to his inclination and ability, to the experiments which it
would be necessary to make, and also by informing the public of all they
might discover, so that, by the last beginning where those before them had
left off, and thus connecting the lives and labours of many, we might
collectively proceed much farther than each by himself could do.

I remarked, moreover, with respect to experiments, that they become always
more necessary the more one is advanced in knowledge; for, at the
commencement, it is better to make use only of what is spontaneously
presented to our senses, and of which we cannot remain ignorant, provided
we bestow on it any reflection, however slight, than to concern ourselves
about more uncommon and recondite phenomena:  the reason of which is, that
the more uncommon often only mislead us so long as the causes of the more
ordinary are still unknown; and the circumstances upon which they depend
are almost always so special and minute as to be highly difficult to
detect.  But in this I have adopted the following order:  first, I have
essayed to find in general the principles, or first causes of all that is
or can be in the world, without taking into consideration for this end
anything but God himself who has created it, and without educing them from
any other source than from certain germs of truths naturally existing in
our minds In the second place, I examined what were the first and most
ordinary effects that could be deduced from these causes; and it appears
to me that, in this way, I have found heavens, stars, an earth, and even
on the earth water, air, fire, minerals, and some other things of this
kind, which of all others are the most common and simple, and hence the
easiest to know.  Afterwards when I wished to descend to the more
particular, so many diverse objects presented themselves to me, that I
believed it to be impossible for the human mind to distinguish the forms
or species of bodies that are upon the earth, from an infinity of others
which might have been, if it had pleased God to place them there, or
consequently to apply them to our use, unless we rise to causes through
their effects, and avail ourselves of many particular experiments.
Thereupon, turning over in my mind I the objects that had ever been
presented to my senses I freely venture to state that I have never
observed any which I could not satisfactorily explain by the principles
had discovered.  But it is necessary also to confess that the power of
nature is so ample and vast, and these principles so simple and general,
that I have hardly observed a single particular effect which I cannot at
once recognize as capable of being deduced in man different modes from the
principles, and that my greatest difficulty usually is to discover in
which of these modes the effect is dependent upon them; for out of this
difficulty cannot otherwise extricate myself than by again seeking certain
experiments, which may be such that their result is not the same, if it is
in the one of these modes at we must explain it, as it would be if it were
to be explained in the other.  As to what remains, I am now in a position
to discern, as I think, with sufficient clearness what course must be taken
to make the majority those experiments which may conduce to this end:  but
I perceive likewise that they are such and so numerous, that neither my
hands nor my income, though it were a thousand times larger than it is,
would be sufficient for them all; so that according as henceforward I
shall have the means of making more or fewer experiments, I shall in the
same proportion make greater or less progress in the knowledge of nature.
This was what I had hoped to make known by the treatise I had written, and
so clearly to exhibit the advantage that would thence accrue to the public,
as to induce all who have the common good of man at heart, that is, all who
are virtuous in truth, and not merely in appearance, or according to opinion,
as well to communicate to me the experiments they had already made, as to
assist me in those that remain to be made.

But since that time other reasons have occurred to me, by which I have
been led to change my opinion, and to think that I ought indeed to go on
committing to writing all the results which I deemed of any moment, as
soon as I should have tested their truth, and to bestow the same care upon
them as I would have done had it been my design to publish them.  This
course commended itself to me, as well because I thus afforded myself more
ample inducement to examine them thoroughly, for doubtless that is always
more narrowly scrutinized which we believe will be read by many, than that
which is written merely for our private use (and frequently what has
seemed to me true when I first conceived it, has appeared false when I
have set about committing it to writing), as because I thus lost no
opportunity of advancing the interests of the public, as far as in me lay,
and since thus likewise, if my writings possess any value, those into
whose hands they may fall after my death may be able to put them to what
use they deem proper.  But I resolved by no means to consent to their
publication during my lifetime, lest either the oppositions or the
controversies to which they might give rise, or even the reputation, such
as it might be, which they would acquire for me, should be any occasion of
my losing the time that I had set apart for my own improvement.  For though
it be true that every one is bound to promote to the extent of his ability
the good of others, and that to be useful to no one is really to be
worthless, yet it is likewise true that our cares ought to extend beyond
the present, and it is good to omit doing what might perhaps bring some
profit to the living, when we have in view the accomplishment of other
ends that will be of much greater advantage to posterity.  And in truth, I
am quite willing it should be known that the little I have hitherto