Angle of dip at a place = `theta`, if the angle of dip in a vertical plane making angle `delta` with the magnetic meridian be `theta'` , show that ,
`tantheta':tan theta=secdelta:1`

Explanation

If the true dip angle in magnetic meridian be `theta` , the vertical and horizontal components of earth's magnetic field be V and H , respectively then ,
`tantheta =(V)/(H)`
In a vertical place inclined at angle `delta` with the magnetic meridian , horizontal component of intensity ,
`H'=Hcosdelta` , apparent dip at that plane = `theta` and vertical component = V.
`therefore" " tantheta'=(V)/(H')=(V)/(Hcosdelta)=tantheta.secdelta`
`"or, "(tantheta')/(tantheta)=secdelta`
`therefore" " tantheta' : tan theta = secdelta:1`