阅读理解
Before the invention of hair dryer,vacuum cleaners were being used for the purpose of drying and styling hair. The early vacuum cleaners could draw in air as well as blowing air.So,towards the end of the 19th century,women used to dry their hair by using a vacuum cleaner.
In 1890,a French salon owner Alexander F.Godefroy invented the first hair dryer.It blew warm air.However,it was not widely used,mainly because of its large size.
The first convenient hand-held hair dryer used at home came up in 1920.It weighed over 2 lbs.However,it only produced 100 watts of power,which was not enough to dry the hair.After almost ten years came the gas-heated dryers that were widely used in barber shops.However,these dryers produced heat that was harmful to hair and the air from them made people sick,so they were soon gone.
Around the 1940s and 1950s,the helmet（头盔）style electric dryers came into being.Curly hairstyles were popular during that time.Therefore,women used curlers and sat under the dryers to set their curls.Later,the curly style began to drop,and so did the popularity of the helmet style electric dryer.
In the late 1950s,the first workable hair dryer was made.It had a hand-held dryer.It used only 300-400 watts. Ever since the 1950s,hand-held dryers have experienced many changes,in order to become quieter,lighter and smaller.However,how it works largely remains the same.The modem technology has made improvements to the hair dryer,reducing the heat damage to a person's hair.For producing shinier,smoother and healthier hair,dryers have been included with negative ion（负离子）technology that dries hair faster and with less heat.
