A combination of assumed or proved facts and circumstances,stated in such form as to constitute a coherent and specific situation or state of facts, upon which the opinion of an expert is asked, by way of evidence on a trial. Howard v. People, 185 111. 552, 57 N. E. 441; People v. Durrant, 116 Cal. 216, 48 Pac. 85; Cowley v. People, 83 N. Y. 464, 38 Am. Rep. 464; Stearns v. Field, 90 N. Y.