THE METHODS OF SCIENCE 95

nothing in common save the absence of x, then x is the

cause of y.

If we subtract from a given effect all that is due to

certain causes, then the residue is the effect of the rest of

the causes. This is the fourth method "that of residues."

Fifthly, and lastly, if x and y increase, decrease, and vary

together, then one is the cause of the other or is closely

connected with such cause. This is called " the method

of concomitant variations."

Objection has been made to the validity of such reason-

ings on the ground that the universe is never the same in

all particulars save one, at any two successive instants,

and that two instances of any event or fact have never

occurred with only one circumstance in common. These

theoretical objections may also be urged not only against

the above " methods," but against all investigations by

experiment and observation.

The objection is no doubt formally correct. The

celestial bodies are never in the same position for two

successive instants, while, on the other hand, their exist-

ence persists through whatever series of experiments we

carry on.

In all cases also there are, and must be, both a multitude

of persistences and a multitude of changes, no one of which

we may ever become aware of. But although such theo-

retical inadequacies must be admitted to exist in every such

proof, they can in most cases be sufficiently well allowed

for, to serve all practical purposes.

The existences of the pleiades, or even of the mountains

in the moon, can be tranquilly ignored while we are trying

experiments with respect to the solidification of gases, nor

do the gavials of the Ganges interfere with careful investi-

gations into the development of the amphioxus or the

apteryx.

nothing in common save the absence of x, then x is the

cause of y.

If we subtract from a given effect all that is due to

certain causes, then the residue is the effect of the rest of

the causes. This is the fourth method "that of residues."

Fifthly, and lastly, if x and y increase, decrease, and vary

together, then one is the cause of the other or is closely

connected with such cause. This is called " the method

of concomitant variations."

Objection has been made to the validity of such reason-

ings on the ground that the universe is never the same in

all particulars save one, at any two successive instants,

and that two instances of any event or fact have never

occurred with only one circumstance in common. These

theoretical objections may also be urged not only against

the above " methods," but against all investigations by

experiment and observation.

The objection is no doubt formally correct. The

celestial bodies are never in the same position for two

successive instants, while, on the other hand, their exist-

ence persists through whatever series of experiments we

carry on.

In all cases also there are, and must be, both a multitude

of persistences and a multitude of changes, no one of which

we may ever become aware of. But although such theo-

retical inadequacies must be admitted to exist in every such

proof, they can in most cases be sufficiently well allowed

for, to serve all practical purposes.

The existences of the pleiades, or even of the mountains

in the moon, can be tranquilly ignored while we are trying

experiments with respect to the solidification of gases, nor

do the gavials of the Ganges interfere with careful investi-

gations into the development of the amphioxus or the

apteryx.