Speculators - thermostats or thermometers?

(Disclaimer : I am not nor have I ever been a speculator. I do have an MBA in Economics (minor Finance) but have never worked in either an economic or financial position.)

I have been troubled for many years by allegations made by politicians, some economists and financial writers that the actions of speculators are the cause of the rise in prices – especially oil. I have spoken to and corresponded with such people in an effort to ascertain whether their statements are true.  So far, the best response I got was an “appeal to authority” by a New York papers financial columnist. 

For any “trolls” reading this diary, let me explain the difference between a thermostat and a thermometer. A thermostat is a device that is used to regulate temperature. A thermometer is a device that shows the themperature.

If speculators are thermostats, their actions would have an effect on prices. However, if they are thermometers, they only report on the effects of other actions on prices.

From what I have been able to determine, speculators are thermometers – thermometers that forecast future events, yes, but only thermometers. 

If anyone can show credible proof that speculators are thermostats, please produce your evidence.