Time Cat: The Remarkable Journeys of Jason and Gareth is a children's book by Lloyd Alexander, first published in 1963. It was his first children's book, and following it he decided to stick with writing for kids, something at which he turned out to be quite good.

The book starts with Jared in his room (punishment for hitting his brother) with his cat, Gareth. To Jared's unsurprise, Gareth reveals that he can speak, and says he has not nine lives, but the ability to 'visit nine lives'. He agrees to take Jared with him, and they proceed to visit Ancient Egypt, the Romans, early beginning of the American Revolution, along with six other places in history.

This book is clearly intended to be educational, and for young enough kids, it would be so. However, as an adult, I found it quite uninteresting. Because the two title characters keep moving to the next place, it more resembles znine short stories, each with their own plot, than one overarching plot.

Egypt: 2700 bce
The travelers meet the pharaoh and teach him that you can't order cats around.
Rome and Britain (55 bce)
Jared joins the Roman legion, and invade Gaul. They then are captured by the 'savages', who turn out all right and who are fascinated by the cat.
Ireland (411 ce)
They meet Diahan, the daughter of King Mogh, and are asked to become the new magician after Gareth saves her from a snake--merely a spirit of a snake according to the current magician. They also come across Sucat--a.k.a. Saint Patrick--who decides to drive out the serpents of war and ignorance.
Japan (998)
Jason becomes Master of Imperial Cats, and Gareth helps raise the kittens recently acquired by young Emperor Ichigo.
Italy (1468)
Our heroic travelers visit a teenaged Leonardo da Vinci and help him convince his father to let him study art.
Peru (1555)
Jason and Gareth meet Don Diego Fransisco Herna'ndez del Gato Herrera y Robles, an unhappy conquistador, and they help him make peace with the Incas.
The Isle of Man (1588)
The travelers meet a sea cat who got caught in a shipwreck.
Germany (1600)
With the help of a friendly blacksmith and a kind lady, the travelers evade those who would kill all cats they can find.
America (1775)
Jared and Gareth meet Professor Parker, a traveling salesman, and no great friend to the British.

Interesting note: he also wrote a Welsh visit, but he ended up turning it into The Prydain Chronicles (which are quite worth reading). At least, that's what Tlachtga tells me.

ISBN: 0-439-72813-4