" The question was before the Iowa Supreme Court again in Keeney v. Arp De La Gardee, 212 Iowa 45, 235 N.W. 745, 748. A jury instruction (referred to as No. 8) was given by the trial court in substantially the same form as that heretofore referred to in Whitaker v. Parker, and included the statement that "while it is proper to consider such evidence, [expert testimony on handwriting] and it is proper to remark that it is the lowest order of evidence or evidence of the most unsatisfactory character, being in fact the result only of a comparison of the controverted with the genuine signature of the defendant and is less satisfactory in character than is positive testimony and such as ought not overthrow the positive and direct testimony of a credible witness who testifies from personal knowledge, but it is most useful in cases of conflict between witnesses, as corroborating testimony." The complaint was, as it was in the Whitaker case, that the instruction was unduly hostile to expert testimony and to the weight to be given thereto.
In Keeney v. De La Gardee, 212 Iowa 45, 235 N.W. 745, the court said: "By microscopic inspection, and by magnified photographs and sometimes by chemical tests, the expert may be able to discover and to demonstrate the existence of facts which negative the genuineness of the signature.
The facts shown in support of the conclusions must be deemed substantive evidence rather than mere expert opinion. Keeney v. Arp De. La Gardee (Evans, J.), 212 Iowa 45, 53, 235 N.W. 745, 749; Brien v. Davidson, 225 Iowa 595, 600, 281 N.W. 150, 282 N.W. 480. See also State v. Wickett, 230 Iowa 1182, 1190, 300 N.W. 268, 272.
We have in other cases held that witnesses with such experience as judges of handwriting were qualified to give opinions as experts under Code section 11278. See Hyde v. Woolfolk Bacon, supra (1 (Clarke) Iowa 159, 165); Hammond v. Wolf, 78 Iowa 227, 231, 42 N.W. 778; Christman v. Pearson, 100 Iowa 634, 69 N.W. 1055; State v. Farrington, supra ( 90 Iowa 673, 680); Keeney v. De La Gardee, 212 Iowa 45, 235 N.W. 745. He was competent to give his opinion. As said in Hyde v. Woolfolk Bacon, supra ( 1 Iowa 159, 167): "Skill in judging of handwriting is common to men of many callings, although one calling may produce a better expert on this subject than another.
" We recognized the advance in the field of expert testimony when, in Keeney v. De La Gardee, 212 Iowa 45, 235 N.W. 745, Judge Evans, speaking for the court, had this to say (page 53 of 212 Iowa, page 749 of 235 N.W.): "We are not unmindful of the fact that, since our original pronouncement in the Whitaker case, 42 Iowa 586, much progress has been made in the means and methods of detecting forgeries.
[9] It is, we think, highly improper to attempt impeachment of a witness by insinuations or slurs, or indirection, but such impeachment should be accomplished, if at all, in a manner provided by law. Keeney v. De La Gardee, 212 Iowa 45, 235 N.W. 745. While we feel it would have been proper to show the witness was not testifying for the plaintiff, in an official capacity, we are convinced that the court did not abuse its discretion in sustaining the question in the form presented. Regardless of this holding, we believe it could not be prejudicial error, for the so-called rebuttal testimony of Mahnke merely corroborated the testimony of witness Preuss, and the photographs in evidence as exhibits, that there was a clear view of approaching vehicles from the south and west toward the road intersection from the point witness Preuss claimed he observed when the accident occurred.
We may repeat that proponent's expert witnesses base their opinions upon comparison of signatures. See Keeney v. De la Gardee, 212 Iowa 45. [3] III. The court told the jury in Instruction Number 10 that if the signatures of decedent and of the subscribing witnesses to at least one of the duplicates were genuine they should find for proponent.