ments being given, was in fault; whether one invention was an
infringement of another, looking at the models of both; and other
cases already mentioned.

This is as near to an exact definition of who are admissible as
experts as it is possible for us to come. In all these cases it is to
be observed that the expert is to speak from no knowledge of the
particular facts which he may happen to possess, but is to pronounce
the judgment of skill upon the particular facts proved by other
witnesses. Of course the court must be first satisfied that the
witness offered is a person of such special skill and experience, for
if he be not, he can give no proper assistance to the jury; and of
course, also, very much must at least be left to the discretion of the
court, relative to the need of such assistance in the case; for very
often the matter investigated may be so bunglingly done that the most
common degree of observation may be sufficient to judge it.

Where a witness is called to testify to handwriting, from knowledge of
his own, however derived, as to the hand of the party, he is not an
expert, but simply a witness to a fact in the only manner in which
that fact is capable of proof. Nor is he an expert who is called to
compare a test writing, whose genuineness is established by others,
with the writing under investigation, if he have knowledge of the
handwriting of the party, because his judgment of the comparison will
be influenced more or less by his knowledge, and will not be what the
testimony of an expert should be, a pure conclusion of skill.

But when a witness, skilled in general chirography, but possessing no
knowledge of the handwriting under investigation, is called to compare
that writing with other genuine writings that have been brought into
juxtaposition with it, he is strictly an expert. His conclusions then
rest in no degree on particular knowledge of his own, but are the
deductions of a trained and experienced judgment, from premises
furnished by the testimony of other witnesses.

One of the palpable anomalies of the present practice regarding
experts on handwriting is that a person who has seen another write, no
matter how ignorant the observer may be, is competent to testify as to
whether or not certain writing is by the hand of the person he has
once seen engaged in the art of writing, while an expert handwriting
witness may only testify that the hand appears to be simulated but may
not point out the d