THE discussion in this note is applicable to vibration pro-*tection of any precision equipment, but optical equipment is particularly susceptible to vibrations. When the supporting structure of a critical component responds in one of its resonant modes, an angular motion probably will result, and an optical beam will magnify this motion. The conventional approach to this problem is to a) place the equipment in a vibration quiet area, b) conduct the experiment during a time of day or night when the dynamic disturbances are at a minimum, and/or c) place the equipment on vibration-isolated test piers. Although such actions usually result in an improvement, two basic facts should be clearly recognized: 1) there is no such thing as a vibration quiet location, and isolation piers merely reduce vibration amplitudes above a certain frequency by a ratio that becomes larger for disturbing vibrations of higher frequencies; and 2) external vibratory forces are transmitted through the air as well as through supports. Figure 1 shows some typical vibration recordings taken on a Vacuum Spectrograph when mounted directly on the laboratory floor and when supported on vibration isolators. Oscillogram A shows that there is a predominant 30-cps frequency in the floor. Electric motors operating at nearly 1800 rpm could be the cause of this disturbance. The displacement amplitudes can be estimated as 2 X 10 ~ in. Oscillogram B shows the response of the grating support platform for the unisolated equipment; the 30-cps component of the floor vibrations was amplified to an amplitude of 1 X 10~ in., resulting in an unacceptable blurring of the spectrum under study. Measurements taken on the outside shell of the equipment adjacent