Abstract: In the fluid coupling for connecting the fluid passages of a plug (1) and a socket (2), a valve (33), a valve holder (31) and a spring (32) disposed in a compressed state between the valve (33) and the valve holder (31) are accommodated inside each of the plug (1) and the socket (2) to be connected to each other the plug (1) is inserted into the socket (2), the valve (33) of the plug (1) and the valve (33) of the socket (2) make contact with each other so that the valves (33) are retracted resisting an urging force of the spring (32). This fluid coupling further includes conical members (32, 51) which form a conical external shape along a line connecting the outside diameter portion of the valve (33) and the outside diameter portion of the valve holder (31) when the valve (33) of the plug (1) and the valve (33) of the socket (2) make contact with each other, so that the springs (32) are compressed between the valve (33) and the valve holder (31).

Abstract: [Problems] To provide a low pressure loss type fluid coupling having a valve holder which has a large effective opening area and never drops the strength thereof. [Means to Solve] In the fluid coupling for connecting the fluid passages of the plug 1 and the socket 2, a valve 33, a valve holder 31 and a spring 32 disposed in a compressed state between the valve 33 and the valve holder 31 are accommodated inside each of a plug 1 and a socket 2 to be connected to each other liquid-tightly, and when the plug 1 is inserted into the socket 2, the valve 33 of the plug 1 and the valve 33 of the socket 2 make contact with each other so that the valves 33 are retracted resisting an urging force of the spring32.

Abstract: In order to provide an underwater microscope which can obtain a sharp picture of live underwater microorganisms in motion, an underwater microscope 10 comprises at least a camera 12 having an optical axis of an optical system, a channel 22 introducing a water sample, a sample chamber 16 having a thickness ranging from 0.