1. Medical thermometer

 

1. Medical thermometer

Source: PixabayThermometers are so ubiquitous today, yet we are not exactly sure who invented the device. Gabriel Fahrenheit first invented the mercury thermometer in 1714, which is still in usage today. However, the first device used to measure temperature appeared in the 1500s and was created by Galileo.

The device was based on the simple principle that a liquid’s density changes with respect to its temperature. Nevertheless, mercury thermometers are being phased out in favor of the digital thermometer due to the poisonous nature of mercury.  

2. Stethoscope

Source: Dr.Farouk/Flickr

Before the stethoscope was invented, doctors would listen to their patient's heartbeats by putting their ear on to their chests, a quite crude and inefficient method. For instance, if there was considerable insulation between the actual heart and exterior of his chest in the form of fat, this method failed.

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French physician René Laënnec faced a similar situation when he couldn't accurately judge one of his patients' heart rates on account that the patient had too much fat on him. He invented the 'stethoscope,' creating a trumpet-shaped wooden tube that amplified sounds coming from lungs and heart. That principle of sound amplification has yet to change.