Which chordate characteristic is visible on the outside of an adult cat?

The spine (or vertebrae) is visible on the posterior (dorsal) part of the cat's body. This is actually due to the bony spinous processes of each vertebra projecting out, which serve to protect the spinal cord and also allow body movements by muscle attachments.

Barometer measures air pressure. They can be used to determine the weather since cold fronts change atmospheric air pressure.

temperature measures heat

tiltmeter measures changes in angle.

hydrometer detects moisture levels.