A thermometer, (a/the) instrument for measuring temperature, can be found in any home.
I can't decide which article to use with 'instrument'.
There are other devices for measuring temperature. We know how hot the sun is, but it would melt any glass tubed instrument.I'd vote for "the" as it's the only instrument fot measuring temperature.
You cannot mix the indefinite and the definite article like this.A thermometer, the instrument for measuring termperature, can be found in any home.
I believe it depends on whether the speaker expects the listener to know what a thermometer is normally used for or not. Then if the information contained in the apposition fragment is new, 'a' is used, if it is known 'the' is used. Do you agree?
2/ this is a definition of a new object so that "the" cannot be used here. Furthermore one cannot mix the indefinite and the definite article like this:
Code:A thermometer, the instrument for measuring termperature, can be found in any home.
Code:http://www.yourdictionary.com/thermometer http://dictionary.reference.com/browse/thermometer http://www.askoxford.com/concise_oed/thermometer?view=uk