Show invention tests testa air the burls london air service has an ingo ilous instrument for lug ing the depth of fog above the starting place tit nt croydon Cr odon or Ab beville and so ho to whether there Is clear dry a few hundred leet feet up tip the instrument which la Is based on file property of human hair of contracting oil tr sharply i on passing from froin wet vet to to dry ner consists of n imir attached to 11 trigg r that holds it 11 ring the dinst ill Is 19 anit aloft niall toy idill loons Is on oll 11 str estilus IlIg ns As ns as it rea re aclus clies dry till the hair li ir contracts pulls pulli the tiller mer aind don comps the ring on the string youths companion |