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To this may be added the further illumination of observations in the courts of appeals. In Christensen v. United States, 259 F. 2d 192, 193, the Court of Appeals for the District of Columbia Circuit said:
Taking into account the detailed description of appellant secured through the advance "tip" along with the detective's observations of appellant's appearance and conduct * * * we hold that there was probable cause for the officer to make the arrest. We cannot view the advance "tip" information and the observations 6f the police detective in two separate logic-tight compartments. Neither one standing alone would constitute probable cause, but together they composed a picture meaningful to a trained, experienced observer.
And in Bell v. United States, 254 F. 2d 82, 85 (C.A.D.C.), Judge Prettyman noted that suspicion on reasonable grounds is not the "mere suspicion" denounced in Mallory v. United States, 354 U.S. 449, 454, and stated (254 F. 2d at 85-86):
[Officers] do not schedule their steps in the calm of an office. Things just happen. They are required as a matter of duty to act as reasonably prudent men would act under the circumstances as those circumstances happen. * * *
*****
[The] action [of an officer experienced in the narcotics traffic] is not measured by what might be probable cause to an untrained civilian passerby. When a peace officer makes the arrest, the standard means a reasonable, cautious and prudent peace officer. The question
