When I was a practice teacher in amiddle school，the students in my class were always making troubles，and had no interest in chemistry.So I made up my mind to do something to change their attitude towards chemistry.

　　The evening before Iwould teach all by myself，I told the students that I would show my extra-sensory perception to them.I distributed a piece of paper to everyone，and told them to write a sentence on the paper and hand it in；I could tell what each one had written.All the students said I must be Long-sighted.Then I stood with my back towards them.I did not turn back until they had finished and put all the paper in a cardboard case.

　　If ound that on the paper there were″You are an idiot″，″I want to have a sleep″，and someone wrote his name-it was not his real name，of course.I turned the cardboard case with the bottom towards the students，and told them slowly what each one had written on the paper.The students were astonished，believing that I had learned their hand writings thoroughly in such a short time.

　　I revealed the truth and they were amazed at my ingenuity：There were five columns of students in the classroom，and everycolumn consisted of ten students.I had written serial numbers(from1to50) on every corner of the paper in a chemical reagent that is invisible to naked eyes，and then distributed them to the students according to thesgroupsof their seats.In this way，I knew the serial number of the paper that everyone had got.After the paper was handed in，I applied another chemical reagent onto the corners of the paper.It reacted with the former reagent and a new substance with visible color was produced，thus the serial numbers were revealed！With the help of a table that marked each student＇sexact seat，I could tell them what they had written on the paper！

　　From then on，the students became greatly interested in chemistry，and we became good friends.