(_a_) From one Department to another, upon requisition by the head
of the Department to which the transfer is to be made.
(_b_) From a bureau of the Treasury Department in which business
relating to the customs is transacted to a classified customs district,
and from such a district to such a bureau of the Treasury Department,
upon requisition by the Secretary of the Treasury.
(_c_) From the Post-Office Department to a classified post-office,
and from such an office to the Post-Office Department, upon requisition
by the Postmaster-General.
2. No person may be transferred as herein authorized until the
Commission shall have certified to the officer making the transfer
requisition that the person whom it is proposed to transfer has passed
an examination to test fitness for the place to which he is to be
transferred, and that such person has during at least six months
preceding the date of the certificate been in the classified service of
the Department, customs district, or post-office from which the transfer
is to be made: _Provided_, That no person who has been appointed
from the copyist register shall be transferred to a place the salary of
which is more than $900 per annum until one year after appointment.