two preferred embodiments of the present invention are hereafter described . however , the invention is not confined to these embodiments . one of the two preferred embodiments is an integrated - type device intended for dynamically measuring the bubble content of a flowing liquid and which is installed in the mixed oil conveyance passage of a mixer for mixing a lubricating oil with a polymer . the device includes a pressure sensor 5 , a pressure calculation circuit 6 , a temperature sensor 7 , a temperature calculation circuit 8 , a volumetric flowmeter 9 , a volumetric flow amplifier 30 , a mass flowmeter 10 , a mass flow amplifier 31 , pressure regulation valves 11 , passage changeover valves 12 , a bubble content calculation circuit 13 which operates in accordance with bubble content calculation formulae ( 1 ) and ( 2 ) above , a control panel 14 , a bubble content display panel 15 , a pressure display panel 16 and a temperature display panel 17 , as shown in fig1 and 2 . these components are provided in housing box 18 . the pressure sensor 5 , the temperature sensor 7 , the volumetric flowmeter 9 , the mass flowmeter 10 , the pressure regulation valves 11 and the passage changeover valves 12 are connected to each other by pipes as shown . the housing 18 is provided in the conveyance passage 1 of the mixer in such a manner that the pipes of the device are connected to the passage by pipe joints a . the sensors 5 and 7 , the flowmeters 9 and 10 , the flow amplifier 30 and 31 , the calculation circuits 6 , 8 and 13 , and the panels 14 , 15 , 16 and 17 are electrically coupled together by wires . the control panel 14 can be manipulated in front of the device . the values shown on the bubble content display panel 15 , the pressure display panel 16 and the temperature display panel 17 can be seen in front of the device . the second embodiment is a separate type device intended for dynamically measuring the bubble content of a flowing liquid and which is installed in a bypass of the lubricating oil conveyance passage of a 2 , 000 cc four - cycle engine for a motor vehicle . the device includes a pump 3 having a function of circulating the liquid in the pump , a connection pipe 4 , a high - pressure section including a pressure sensor 5 , a pressure calculation circuit 6 , a temperature sensor 7 , a temperature calculation circuit 8 , a volumetric flowmeter 9 , a volumetric flow amplifier 30 , a pressure regulation valve 11 , a bubble content calculation circuit 13 operating in accordance with calculation formula ( 1 ) above , a bubble content display panel 15 , a pressure display panel 16 and a temperature display panel 17 , a low - pressure section including a pressure sensor 5 , a pressure calculation circuit 6 , a temperature sensor 7 , a temperature calculation circuit 8 , a volumetric flowmeter 9 , a volumetric flow amplifier 30 , a pressure regulation valve 11 , a bubble content calculation circuit 13 operating in accordance with calculation formula ( 2 ), a bubble content display panel 15 , a pressure display panel 16 and a temperature display panel 17 , a mass flowmeter 10 , a mass flow amplifier 31 , and a control panel 14 , as shown in fig3 and 4 . these components are provided in housing boxes 18 . two tapped holes are provided in the lubricating oil conveyance passage 1 of the engine . the bypass 2 is connected to the passage by pipe joints a screw - engaged in the tapped holes . the sensors , the calculation circuits , the flowmeters , the flow amplifiers and the panels are electrically coupled together by wires so that the device is composed of a bubble content measuring detector 19 connected to the bypass 2 , and a bubble content measuring data processor 20 electrically coupled to the detector . with the device of the present invention , a flowing liquid containing bubbles does not need to be extracted from a passage for the liquid for measuring the bubble content of the liquid . for this reason , the bubble content can be measured as the liquid remains flowing in the passage . moreover , the bubbles do not disappear by the measurement . since pressure regulation valves , a volumetric flowmeter , a mass flowmeter and so forth are provided and novel calculation formulae are employed , the bubble content can be dynamically , quickly and accurately measured not only at high pressure , as in the conventional case , but also at low pressure , and the bubble quantity of the dissolved gas in the liquid due to a change in the pressure thereof can be dynamically , quickly and accurately measured . the bubble content measuring detector of a separate type device such as the second embodiment can be used in a severe environment of high or low temperature , while the bubble content measuring data processor of the device can be used in a normal environment . for this reason , the range of use of the device is wide . since a pump having a function of circulating the liquid is provided to pulverize the bubbles in the liquid at the time of introduction of the liquid into the device to uniformly disperse the pulverized elements of the bubbles , the dispersion in the measured value of the bubble content of the liquid is reduced . although it is difficult to obtain accurate data as to the bubble content of a flowing liquid in a conventional device , the bubble content can be continuously measured under various conditions in accordance with the present invention to make it easier to control the quality of each of various kinds of liquids . the present invention can be utilized for research as well as for practical use . since the maximum rotational speeds of automobile and motorcycle engines have recently been increased , the bubble content of the lubricating oil for the engine has become very large . the bubbles are likely to do various kinds of harm to the hydraulic mechanism and sliding surfaces of the engine . however , since there has not been a method for quickly and accurately measuring the bubble content of the lubricating oil under various conditions during the actual flow of the oil , it was difficult to fully clarify the quantitative relationship between the bubble content and the degree and type of the damage . the present invention can be applied for such full clarification in research .