1. Whenever any officer having the power of appointment or employment shall so request, there shall be certified to him by the Commission or the proper examining board four names for the vacancy specified, to be taken from those graded highest on the proper register of those in his branch of the service and remaining eligible, regard being had to the apportionment of appointments to States and Territories; and from the said four a selection shall be made for the vacancy. 2. These certifications for the service at Washington shall be made in such order as to apportion, as nearly as may be practicable, the original appointments thereto among the States and Territories and the District of Columbia upon the basis of population as ascertained at the last preceding census. 3. In case the request for any such certification or any law or regulation shall call for those of either sex, the four highest of that sex shall be certified; otherwise sex shall be disregarded in such certification. 4. No person upon any register shall be certified more than three times to the same officer in the customs or postal service or more than twice to any department at Washington, unless upon request of the appointing officer; nor shall anyone remain eligible more than one year upon any register. And no person while remaining eligible on any register shall be admitted to a new examination of the same grade. RULE XVII. 1. Every original appointment or employment in said classified service shall be for the probationary period of six months, at the end of which time, if the conduct and capacity of the person appointed have been found satisfactory, the probationer shall be absolutely appointed or employed, but otherwise be deemed out of the service. 2. Every officer under whom any probationer shall serve during any part of the probation provided for by these rules shall carefully observe the quality and value of the service rendered by such probationer, and shall report to the proper appointing officer, in writing, the facts observed by him, showing the character and qualifications of such probationer and of the service performed by him; and such reports shall be preserved on file. 3. Every false statement knowingly made by any person in his application for examination and every connivance by him at any false statement made in any certificate which may accompany his application shall be regarded as good cause for the removal or discharge of such person during his probation. RULE XVIII.