Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

345 OF ENGINEERING FORMULÆ. Electrical Formulae, by Paget Higgs, LL.D., C.E.— continued. which R must be a considerable multiple), f = distance between axes of R' and R, where 1 210^l is usual concentric form. 41. To reduce current flowing through galvan- ometer to its -th part, insert a shunt whose resistance is th part of g. The compensating . , , n — 1 g2 resistance will be g-----= —------- n g + s 42. Correction for readings on mirror galv.: : s2:: d2 (V z2 + A — «): dt z2 + - z) d = deflection ; z = distance of mirror from scale in divisions of scale. , „ _ amplitude of a vibration 43. The log. of —-j—----—— -----------= a = that next following logarithmic decrement. If Cj is amplitude of 1st and C» that of nth vibration, then